WASHINGTON - The deadly attack at the Washington Navy Yard was carried out by one of the military's own: a defence contract employee and former Navy reservist who used a valid pass to get onto the installation and started firing inside a building, killing 12 people before he was slain in a gun battle with police.

The motive for the mass shooting — the deadliest on a military installation in the U.S. since the tragedy at Fort Hood, Texas, in 2009 — was a mystery, investigators said. But a profile of the lone gunman, 34-year-old Aaron Alexis, was coming into focus. He was described as a Buddhist who had also had flares of rage, complained about the Navy and being a victim of discrimination, and had several run-ins with law enforcement, including two shootings.

The latest mass shooting quickly reignited the debate over gun control in the United States. President Barack Obama lamented "yet another mass shooting" in the U.S. and promised to make sure "whoever carried out this cowardly act is held responsible." Obama has been powerless to get gun control legislation passed by Congress amid a fierce backlash from conservative politicians and the gun owners lobby.

Monday's onslaught at a single building at the highly secure Navy Yard unfolded about 8:20 a.m. in the heart of the U.S. capital, less than four miles (6.4 kilometres) from the White House and two miles (3.2 kilometres) from the Capitol.

It put all of Washington on edge. Mayor Vincent Gray said there was no indication it was a terrorist attack, but he added that the possibility had not been ruled out.

"This is a horrific tragedy," he said.

Alexis carried three weapons: an AR-15 assault rifle, a shotgun, and a handgun that he took from a police officer at the scene, according to two federal law enforcement officials who spoke on condition of anonymity because they were not authorized to discuss the investigation.

The AR-15 is the same type of rifle used in last year's mass shooting at a Newtown, Connecticut, elementary school that killed 20 students and six female staffers. The weapon was also used in the shooting at a Colorado movie theatre that killed 12 and wounded 70.

It was far from certain what impact the latest mass shooting would have on the debate over gun control in the United States.

The politics of gun control have only gotten tougher since December's shooting at Connecticut's Sandy Hook Elementary School. That shooting spurred Obama to propose stricter firearms laws that failed to pass in the Senate.

White House spokesman Jay Carney on Monday reiterated the Obama administration's commitment to strengthening gun laws, including expanding background checks to sales online and at gun shows.

Gun owners, aided by their advocates at the National Rifle Association, the country's largest gun rights lobby, have successfully fought Obama's legislation, even though polls show broad support for tougher gun laws.

For much of the day, authorities said they were looking for a possible second attacker who may have been disguised in an olive-drab military-style uniform. But by late Monday night, they said they were convinced the shooting was the work of a lone gunman, and the lockdown around the area was eased.

"We do now feel comfortable that we have the single and sole person responsible for the loss of life inside the base today," Washington police Chief Cathy Lanier said.

The FBI took charge of the investigation.

The attack came four years after Army psychiatrist Maj. Nidal Hasan killed 13 people at Fort Hood in what he said was an effort to save the lives of Muslims overseas. He was convicted last month and sentenced to death.

In addition to those killed at the Navy Yard, eight people were hurt, including three who were shot and wounded, according to the mayor. Those three were a police officer and two female civilians, authorities said. They were all expected to survive.

The dead ranged in age from 46 to 73, according to the mayor. A number of the victims were civilian employees and contractors, rather than active-duty military personnel, the police chief said.

At the time of the rampage, Alexis was an employee with The Experts, a company that was a Defence Department subcontractor on a Navy-Marine Corps computer project, authorities said.

Valerie Parlave, head of the FBI's field office in Washington, said Alexis had access to the Navy Yard as a defence contractor and used a valid pass.

Alexis had been a full-time Navy reservist from 2007 to early 2011, leaving as a petty officer third class, the Navy said. It did not say why he left. He had been an aviation electrician's mate with a unit in Fort Worth.

A convert to Buddhism who grew up in New York City, Alexis had had run-ins with the law over shooting incidents in 2004 and 2010 in Fort Worth and Seattle and was portrayed in police reports as seething with anger.

The Washington Navy Yard is a sprawling, 41-acre (16.6-hectare) labyrinth of buildings and streets protected by armed guards and metal detectors, and employees have to show their IDs at doors and gates. More than 18,000 people work there.

The rampage took place at Building 197, the headquarters for Naval Sea Systems Command, which buys, builds and maintains ships and submarines. About 3,000 people work at headquarters, many of them civilians.

Witnesses on Monday described a gunman opening fire from a fourth-floor overlook, aiming down on people on the main floor, which includes a glass-walled cafeteria. Others said a gunman fired at them in a third-floor hallway.

Patricia Ward, a logistics-management specialist, said she was in the cafeteria getting breakfast.

"It was three gunshots straight in a row — pop, pop, pop. Three seconds later, it was pop, pop, pop, pop, pop, so it was like about a total of seven gunshots, and we just started running," Ward said.

Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and co-workers encountered a gunman in a long hallway on the third floor. The gunman was wearing all blue, he said.

"He just turned and started firing," Brundidge said.

Terrie Durham, an executive assistant with the same agency, said the gunman fired toward her and Brundidge.

"He aimed high and missed," she said. "He said nothing. As soon as I realized he was shooting, we just said, 'Get out of the building.'"

As emergency vehicles and law enforcement officers flooded the streets, a helicopter hovered, nearby schools were locked down and airplanes at Reagan National Airport were grounded so they would not interfere with law-enforcement choppers.

Security was tightened at other federal buildings. Senate officials shut down their side of the Capitol. The House of Representatives remained open.

After authorities determined late Monday that the available evidence indicated the deceased shooter acted alone, Sergeant at Arms Terrance Gainer said all operations at the Senate would return to normal Tuesday.

In the confusion, police said around midday that they were searching for two accomplices who may have taken part in the attack — one carrying a handgun and wearing a tan Navy-style uniform and a beret, the other armed with a long gun and wearing an olive-green uniform. Police said it was unclear if the men were members of the military.

But as the day wore on, police dropped one person and then the other as suspects. As tensions eased, Navy Yard employees were gradually released from the complex, and children were let out of their locked-down schools.

Adm. Jonathan Greenert, chief of naval operations, was at the base at the time the shooting began but was moved unharmed to a nearby military installation.

___

Associated Press writers Jesse Holland, Stacy A. Anderson, Brian Witte and Ben Nuckols in Washington contributed to this report.

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  • Navy Yard Shooter Alleged Suspect Aaron Alexis

    UNKNOWN, UNSPECIFIED - SEPTEMBER 16: In this handout photo provided by the FBI, Aaron Alexis is shown in a photo prior to the mass shooting at the Washington Navy Yard on September 16, 2013 in Washington, D.C. Authorities believe Alexis was a gunman involved in the shootings at the Navy Yard, where at least 12 people were shot and killed. (Photo by FBI via Getty Images)

  • Family and friends wait to greet staff of the Naval Sea Systems Command headquarters as they are bused from the Washington Navy Yard to Nationals Park, in Washington, Monday, Sept. 16, 2013. At least one gunman launched an attack inside the Washington Navy Yard, spraying gunfire on office workers in the cafeteria and in the hallways at the heavily secured military installation in the heart of the nation's capital, authorities said. (AP Photo/Jacquelyn Martin)

  • US-MILITARY-SHOOTING

    Police conduct an investigation into a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 13 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Nii Oti-Ankrah, left, kisses his wife Sally Appiah-Ankrah as he holds their son Eilam Ankrah after she was evacuated from building 197 at the Washington Navy Yard, Monday Sept. 16, 2013 in Washington. At least one gunman launched an attack inside the Washington Navy Yard, spraying gunfire on office workers in the cafeteria and in the hallways at the heavily secured military installation in the heart of the nation's capital, authorities said. (AP Photo/Alex Brandon)

  • An officer who said he works for the Department of Defense, right, checks an id outside of the closed Washington Navy Yard in Washington, on Tuesday, Sept. 17, 2013, the day after a gunman launched an attack inside the Washington Navy Yard on Monday, spraying gunfire on office workers in the cafeteria and in the hallways at the heavily secured military installation in the heart of the nation's capital. Only essential personnel were being permitted inside, according the authorities. (AP Photo/Jacquelyn Martin)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Family members of Navy Yard complex employees gather outside a parking lot that was converted to a point of reunion at Nationals Park in the wake of the Navy Yard shooting September 16, 2013 in Washington, DC. Police believe at least one gunman shot and killed 12 people and wounded others in an incident that put parts of the city on lockdown. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: A woman hugs her child while reuniting at a gathering point for family members of Navy Yard employees that was set up inside Nationals Park in the wake of the shooting September 16, 2013 in Washington, DC. Police believe at least one gunman shot and killed at least 12 people and wounded others in an incident that put parts of the city on lockdown. (Photo by Win McNamee/Getty Images)

  • US-MILITARY-SHOOTING

    A Red Cross vehicle arrives at a family gathering point for the Navy Yard shootings set up at parking lot B of Nationals Park on September 16, 2013 in Washington, DC. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 12 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO / Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    A woman steps out of a bus which arrived at parking lot B of Nationals Park which has been set up as a gathering point for families of the Navy Yard shootings on September 16, 2013 in Washington, DC. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 12 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Family members of Navy Yard complex employees gather outside a parking lot that was converted to a point of reunion at Nationals Park in the wake of the Navy Yard shooting September 16, 2013 in Washington, DC. Police believe at least one gunman shot and killed 12 people and wounded others in an incident that put parts of the city on lockdown. (Photo by Win McNamee/Getty Images)

  • US-MILITARY-SHOOTING

    A US marine guards the entrance of a garage building oposite the US Navy yard on September 16, 2013 in Washington.A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 12 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO/MLADEN ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images)

  • A small group holds a candle light vigil on Freedom Plaza to remember the victims of the shooting at the Washington Navy Yard, Monday, Sept. 16, 2013, in Washington. (AP Photo/J. Scott Applewhite)

  • US-MILITARY-SHOOTING

    Police cars are parked outside Navy Yard following a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 13 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    Police work as they investigate a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 13 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Family members of Navy Yard complex employees gather outside a parking lot that was converted to a point of reunion at Nationals Park in the wake of the Navy Yard shooting September 16, 2013 in Washington, DC. Police believe at least one gunman shot and killed 12 people and wounded others in an incident that put parts of the city on lockdown. (Photo by Win McNamee/Getty Images)

  • US-MILITARY-SHOOTING

    Police conduct an investigation into a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage Monday at a US naval base in the heart of Washington claimed at least 13 lives, including the unidentified gunman, while another possible suspect was still at large, police said. The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the US Capitol, home of Congress. US officials gave no indication of any link to terrorism while police said the motive for the attack on the naval installation was unknown. 'At this hour, it appears that we have at least 12 fatalities,' Washington DC police chief Cathy Lanier told a press conference. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: A Park Police helicopter carries a sniper to the roof of a building on the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Atlanta Braves first baseman Freddie Freeman enters Nationals Park, where a staging area for familes involved in the Navy Yard shooting were instructed to gather, and where the Braves were scheduled to play the Washington Nationals September 16, 2013 in Washington, DC. Police believe at least one gunman shot and killed 12 people and wounded others in an incident that put parts of the city on lockdown. The baseball game tonight has been canceled. (Photo by Win McNamee/Getty Images)

  • US-MILITARY-SHOOTING

    Police tactical units leave after responding to a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage at the Washington naval base claimed at least 12 lives including that of an unidentified gunman, city police chief Cathy Lanier told reporters Monday. Lanier said two more potential suspects were still at large after the shooting at the Washington Naval Yard and that the motive of the shooter or shooters was not yet known. 'We are confirming 12 fatalities. We had a few additional victims who were injured. They were not fatally injured,' she said, briefing reporters on a street by the base. Lanier gave more details on two male suspects seen near the scene of the shooting, a headquarters building within the riverside base, who police are hunting. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    Members of the military look out from a nearby building toward police units responding to a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage at the Washington naval base claimed at least 12 lives including that of an unidentified gunman, city police chief Cathy Lanier told reporters Monday. Lanier said two more potential suspects were still at large after the shooting at the Washington Naval Yard and that the motive of the shooter or shooters was not yet known. 'We are confirming 12 fatalities. We had a few additional victims who were injured. They were not fatally injured,' she said, briefing reporters on a street by the base. Lanier gave more details on two male suspects seen near the scene of the shooting, a headquarters building within the riverside base, who police are hunting. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    Police tactical units leave after responding to a shooting at the Navy Yard in Washington, DC, September 16, 2013. A shooting rampage at the Washington naval base claimed at least 12 lives including that of an unidentified gunman, city police chief Cathy Lanier told reporters Monday. Lanier said two more potential suspects were still at large after the shooting at the Washington Naval Yard and that the motive of the shooter or shooters was not yet known. 'We are confirming 12 fatalities. We had a few additional victims who were injured. They were not fatally injured,' she said, briefing reporters on a street by the base. Lanier gave more details on two male suspects seen near the scene of the shooting, a headquarters building within the riverside base, who police are hunting. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    Unidentified people are seen on September 16, 2013, outside parking lot B of Nationals Park which has been set as a gathering point for families of the Navy Yard shootings in Washington DC. One gunman has been killed and up to two more may still be at large after a shooting rampage at the US Naval base in Washington on Monday that left 'multiple victims' dead, the city's police chief said. 'We have one shooter that we believe involved in this that is deceased,' said Washington police chief Cathy Lanier. 'The big concern for us right now is that we potentially have two other shooters that we have not located at this point.' AFP PHOTO/MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    An unidentified woman is reunited at the family gathering site outside parking lot B of Nationals Park, which has been set as a gathering point for families of the Navy Yard shootings in Washington DC on September 16, 2013. The shooting rampage at a Washington naval base claimed at least 12 lives including that of an unidentified gunman, city police chief Cathy Lanier told reporters Monday. Lanier said two more potential suspects were still at large after the shooting at the Washington Naval Yard and that the motive of the shooter or shooters was not yet known. 'We are confirming 12 fatalities. We had a few additional victims who were injured. They were not fatally injured,' she said, briefing reporters on a street by the base. Lanier gave more details on two male suspects seen near the scene of the shooting, a headquarters building within the riverside base, who police are hunting. AFP PHOTO/MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    Police respond to the report of a shooting at the Navy Yard in Washington, DC, September 16, 2013. At least one unidentified gunman opened fire at the US Navy Yard in Washington on Monday and was at large after killing 'multiple' victims and wounding several more, officials said. Police and FBI agents descended on the area in force as helicopters swarmed overhead, amid reports a shooter was armed with an assault rifle and was holed up at the complex. 'We believe there were multiple deaths,' a US defense official, speaking on condition of anonymity, told AFP. The precise death toll remained unclear, the official said. A Washington DC police officer and another law enforcement officer had been shot while the gunman had allegedly barricaded himself in a room in a headquarters building, media reported.AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • US-MILITARY-SHOOTING

    A US Park Police helicopter patrols over the US Navy yard September 16, 2013 in Washington, DC. At least one unidentified gunman opened fire at the US Navy Yard in Washington on Monday and was at large after killing 'multiple' victims and wounding several more, officials said. Police and FBI agents descended on the area in force as helicopters swarmed overhead, amid reports a shooter was armed with an assault rifle and was holed up at the complex. 'We believe there were multiple deaths,' a US defense official, speaking on condition of anonymity, told AFP. The precise death toll remained unclear, the official said. A Washington DC police officer and another law enforcement officer had been shot while the gunman had allegedly barricaded himself in a room in a headquarters building, media reported. AFP PHOTO/Paul J. Richards (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Emergency vehicles and law enforcement stage at the end of the 11th Street Bridge adjacent to the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Armed police prepare to enter the Washington Navy Yard as they respond to a shooting in Washington, Monday, Sept. 16, 2013. At least one gunman opened fire inside a building at the Navy yard. (AP Photo/Manuel Balce Ceneta)

  • A U.S. Park Police helicopter removes a man in a basket from the Washington Navy Yard Monday, Sept. 16, 2013. Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin)

  • Police work the scene on M Street S.E. in Washington, where a gunman was reported in a military building at the Washington Navy Yard Monday, Sept. 16, 2013. Shots have been fired and employees directed to a shelter. Police and federal agents from multiple law enforcement agencies responded to the scene and streets in the area were closed. (AP Photo/Jacquelyn Martin)

  • A police boat patrols near the scene of a shooting at the Washington Navy Yard on Monday, Sept. 16, 2013, in Washington. At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning. (AP Photo/ Evan Vucci)

  • Cathy Lanier

    District of Columbia Police Chief Cathy Lanier briefs reporters on the shooting at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013, where at least one gunman opened fire inside a building at the Washington Navy Yard. (AP Photo/Susan Walsh)

  • Police respond to the report of a shooting at the Navy Yard in Washington, DC, September 16, 2013. A gunman shot and wounded at least one person Monday in a headquarters building at the US Navy Yard in Washington and is still at large, the navy said.'There is one confirmed injury. Emergency personnel are on scene and a 'shelter in place' order has been issued for Navy Yard personnel,' the navy said in a statement. Local television reported that there were as many as five casualties and the Navy said that police had entered building number 197 in search of the shooter. The Navy said at least three shots were fired at 8:20 am (1320 GMT) in the headquarters building of the Naval Sea Systems Command. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Washington Navy Yard

    A U.S. Park Police helicopter flies over a building at the Washington Navy Yard in Washington, Monday, Sept. 16, 2013. President Barack Obama is mourning what he called "yet another mass shooting" in the United States that he says took the life of American patriots. (AP Photo/Susan Walsh)

  • Police Work The Scene

    Police work the scene on M Street, SE in Washington, where a gunman was reported at the Washington Navy Yard in Washington, on Monday, Sept. 16, 2013. The U.S. Navy says one person is injured after a shooting at a Navy building in Washington. (AP Photo/Jacquelyn Martin)

  • A U.S. Park Police helicopter removes a man in a basket from the Washington Navy Yard Monday, Sept. 16, 2013. Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin)

  • Police Work The Scene

    Police work the scene on M Street, SE in Washington near the Washington Navy Yard on Monday, Sept. 16, 2013. The U.S. Navy says one person is injured after a shooting at a Navy building in Washington. Police and emergency crews gathered Monday morning outside the Naval Sea Systems Command Headquarters building, where the shooting was reported. (AP Photo/Jacquelyn Martin)

  • Police respond to the report of a shooting at the Navy Yard in Washington, DC, September 16, 2013. A gunman shot and wounded at least one person Monday in a headquarters building at the US Navy Yard in Washington and is still at large, the navy said.'There is one confirmed injury. Emergency personnel are on scene and a 'shelter in place' order has been issued for Navy Yard personnel,' the navy said in a statement. Local television reported that there were as many as five casualties and the Navy said that police had entered building number 197 in search of the shooter. The Navy said at least three shots were fired at 8:20 am (1320 GMT) in the headquarters building of the Naval Sea Systems Command. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Police respond to the report of a shooting at the Navy Yard in Washington, DC, September 16, 2013. A gunman shot and wounded at least one person Monday in a headquarters building at the US Navy Yard in Washington and is still at large, the navy said.'There is one confirmed injury. Emergency personnel are on scene and a 'shelter in place' order has been issued for Navy Yard personnel,' the navy said in a statement. Local television reported that there were as many as five casualties and the Navy said that police had entered building number 197 in search of the shooter. The Navy said at least three shots were fired at 8:20 am (1320 GMT) in the headquarters building of the Naval Sea Systems Command. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Scene At The Gate Of Navy Yard

  • Police respond to the report of a shooting at the Navy Yard in Washington, DC, September 16, 2013. A gunman shot and wounded at least one person Monday in a headquarters building at the US Navy Yard in Washington and is still at large, the navy said.'There is one confirmed injury. Emergency personnel are on scene and a 'shelter in place' order has been issued for Navy Yard personnel,' the navy said in a statement. Local television reported that there were as many as five casualties and the Navy said that police had entered building number 197 in search of the shooter. The Navy said at least three shots were fired at 8:20 am (1320 GMT) in the headquarters building of the Naval Sea Systems Command. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

  • Outside Navy Yard

  • Police Clear Block

  • Looking Up M Street

  • Members of the military guard a military garage near the Washington Navy Yard where a gunman was reported in Washington, on Monday, Sept. 16, 2013. The exact number of people killed and the conditions of those wounded was not immediately known. (AP Photo/Jacquelyn Martin)

  • A helicopter that has been airlifting people from the top of a building at the Washington Navy Yard circles the area after a gunman was reported at the Washington Navy Yard in Washington, on Monday, Sept. 16, 2013. The exact number of people killed and the conditions of those wounded was not immediately known. About 3,000 people work at the Naval Sea Systems Command headquarters. (AP Photo/Jacquelyn Martin)

  • Police bring in equipment by an anchor outside of an entrance to the Washington Navy Yard where a gunman was reported in Washington, on Monday, Sept. 16, 2013. The exact number of people killed and the conditions of those wounded was not immediately known. About 3,000 people work at the Naval Sea Systems Command headquarters. (AP Photo/Jacquelyn Martin)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Construction workers wait at the end of the 11th Street Bridge adjacent to the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Armed ATF agents stage on the 11th Street Bridge adjacent to the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: People shelter in place outside a building at the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: Police boats patrol the water outside a building at the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)

  • Shooting At Washington DC Navy Yard Reportedly Leaves Several Wounded

    WASHINGTON, DC - SEPTEMBER 16: A Park Police helicopter hovers above a building at the Navy Yard complex where a shooting took place early this morning September 16, 2013 in Washington, DC. Early reports indicate that several people may have been shot, and police are still trying to determine the number of suspects involved in the shooting. (Photo by Win McNamee/Getty Images)



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When 13 people died in a shooting rampage at the Washington Navy Yard on Monday, the story made front page news. But many of the mass shootings that have happened since the December massacre of elementary school students and teachers in Newtown, Conn., didn't.

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The Associated Press reports:

Michael Slocum, an attorney for a Virginia gun store, said in an email that Aaron Alexis visited Sharpshooters Small Arms Range on Sunday. He says Alexis rented a rifle, bought bullets and used the range. He then bought a shotgun and 24 shells.

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WASHINGTON -- Alleged Navy Yard shooter Aaron Alexis acted alone and was "determined to kill as many people as possible," law enforcement officials said Tuesday.

Officials would not comment on Alexis' alleged motive during a press conference held Tuesday afternoon outside the FBI's Washington Field Office, but said they had determined he arrived in the area around Aug. 25 and had been staying at the Residence Inn in Southwest Washington, D.C. since Sept. 7.

The FBI is investigating "hundreds" of tips they have received Monday's shooting. "No piece of information is too small," said FBI Assistant Director in Charge Valerie Parlave, asking for additional assistance from the public.

Metropolitan Police Officer Scott Williams is doing well and is expected to make a full recovery, according to MPD Chief Cathy Lanier. "We have a very good prognosis from the doctors, he does have serious injuries to his legs. Again, I know the officer and I know his personality, and I'm real confident he will not only walk again but probably will outrun most of us again," Lanier said.

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Aaron Alexis entered Building 197 with only a shotgun in his possession, not an assault rifle like some media outlets reported. "We have no information that [Alexis] had an AR-15 assault rifle in his possession," the FBI's Valerie Parlave said in a press conference. "He may have gained access to a handgun ... and after he began shooting."

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Alexis was honorably discharged from the Navy in 2011 after bouts of insubordination, disorderly conduct and being absent from work without authorization.

The AP reports:

Officials said the bad conduct was enough to make it clear Alexis would not be a good sailor, but not enough to warrant a general or less-than-honorable discharge. They also did not involve criminal offenses, so did not trigger any court-martial proceedings.

Click here to read more.

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Here's a complete list of the victims of yesterday's shooting:

Michael Arnold, 59
Martin Bodrog, 54
Arthur Daniels, 51
Sylvia Frasier, 53
Kathleen Gaarde, 62
John Roger Johnson, 73
Mary Francis Knight, 51
Frank Kohler, 50
Vishnu Pandit, 61
Kenneth Bernard Proctor, 46
Gerald L. Read, 58

Richard Michael Ridgell, 52

Suspected gunman Aaron Alexis, 34, died as well.

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Dr. Janis Orlowski, chief medical officer at MedStar Washington Hospital Center, told the Associated Press that three victims in yesterday's shooting -- including a police officer who was shot in the legs -- are recovering and in fair or good condition. She said two women who saw others shot are "very worried about their co-workers," but are unaware of the extent of the shooting.

Click here for more.

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Schools near Navy Yard that were on lockdown after Monday's shooting have reopened on Tuesday, WJLA reports.

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"A dozen or so" people gathered for a candlelight vigil at D.C.'s Freedom Plaza last night, reports the Washington City Paper:

"How immune are we becoming to these senseless mass shootings?" Eddie Weingart, the vigil's organizer and the founder of Project End Gun Violence, asked the ceremony's participants, who were flanked by twice as many media members. "Mass shootings are becoming as American as apple pie and baseball."

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NEW YORK -- Rep. Jason Chaffetz's (R-Utah) accusatory tweet is only one example of a meme now making its way through the conservative community: that somehow "political correctness" -- a refusal to judge employees, especially in the military -- is responsible for the Navy Yard shooting.

At a conservative monthly gathering here called the New York Meeting, Rep. Joe Wilson (R-S.C.), who gained notoriety for shouting "you lie" at President Barack Obama, said that the military had failed in recent years to do proper "threat assessments" of individuals, and that the Fort Hood attack in 2009 was the result of the failure to properly supervise the assailant, Nidal Hasan -- and that the same laxity of supervision might have been at work at the Navy Yard.

"There have been six different internal attacks within the military on fellow troops" in recent years, Wilson said. He agreed with a questioner that there had been a "change in the culture" and that "political correctness" had produced an atmosphere of lax supervision.

-- Howard Fineman

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After the Boston Marathon bombing, Reddit users attempted to figure out who the culprits were, leading to "online witch hunts" that resulted in falsely fingering individuals.

On Monday, Reddit took steps to make sure that didn't happen again in the aftermath of the Navy Yard shooting, shutting down a section known as a "subreddit" that sought to identify the shooter.

"We banned it because it violated site rules by encouraging the posting of personal information," Erik Martin from Reddit told the Washington Post. "The quote from the side bar that subreddit [sic] that was banned said 'no personal information about leads unless you are really sure.' We do not allow the posting of personal information under any circumstances."

-- Amanda Terkel

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Navy Yard gunman Aaron Alexis reportedly suffered from "a host of serious mental issues, including paranoia and a sleep disorder ... [and] had been hearing voices in his head," according to the Associated Press.

However, the Navy had not declared him mentally unfit, which would have rescinded his security clearance.

Read more here.

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Navy Yard gunman Aaron Alexis "was described as a Buddhist who had also had flares of rage, complained about the Navy and being a victim of discrimination and had several run-ins with law enforcement, including two shootings," according to the Associated Press.

Washington, D.C. Mayor Vincent Gray called the shooting "a horrific tragedy," but said there was no indication it was a terrorist attack, although the possibility had not been ruled out.

Read more about Alexis' background here.

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Senate Sergeant at Arms Terrance Gainer said after authorities determined the slain Navy Yard shooter acted alone that all operations at the Senate would return to normal on Tuesday.

Read the full story here.

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Slain Washington Navy Yard shooting suspect Aaron Alexis had "secret clearance," the CEO of The Experts Inc. told Reuters.

"He did have a secret clearance. And he did have a CAC (common access card)," said Thomas Hoshko, CEO of The Experts Inc., which was helping service the Navy Marine Corps Intranet as a subcontractor for HP Enterprise Services, part of Hewlett-Packard Co.

Read the full story here.

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The names of seven of the 12 people killed in Monday's shooting at the Washington Navy Yard have been released.

Read the whole story here.

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Meditations on the roots of violence were front and center Monday during an evening prayer service at the Washington National Cathedral.

A layman at the nation's house of worship, Andrew Hullinger, led several dozen worshippers in prayer not only for the victims of Monday's mass shooting at the Washington Navy Yard, but also for "the lost, who seemed to believe that violence was their only option."

Read more of Christina Wilkie's report here.

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Washington police Officer Scott Williams was identified by authorities at a Monday night press conference as having been wounded in the shooting at the Washington Navy Yard earlier in the day.

Read the whole story here.

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Washington Police Chief Cathy Lanier said in a press briefing that "we have the single and sole person responsible" and police are lifting the "shelter in place" order.

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Roads were closed for blocks. Businesses shut down. People in nearby buildings were instructed to stay inside. The Senate went into shutdown mode, planes at nearby airports were grounded, and the Nationals, whose baseball stadium is blocks from the Navy Yard, called off their scheduled evening game against the Braves.

Navy Yard employees -- there are roughly 3,000 of them -- were allowed to leave the complex by 3:30 p.m. Monday, having been on lockdown for hours. And slowly, hundreds began to fill the empty streets and make their way to the nearby Metro station. Some stopped for a few minutes to talk to reporters about their experience.

"Terrifying," said Gregory Dade, who said he locked himself in his office as gunfire carried on for nearly an hour outside his door.

Read more of the report from HuffPost's Jennifer Bendery here.

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Washington Mayor Vincent Grey provided new information in a press conference on the deceased: Their ages are 46 to 73 years of age. Seven families have been notified.

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NBC News reports on the weapons Alexis had with him on Monday:

He packed an assault rifle and two other firearms during his lethal rampage — including a shotgun purchased just weeks ago at a Virginia gun shop, multiple law enforcement officials told NBC News.

The officials also said Alexis obtained the assault rifle used in the shooting from a gun safe on the naval base. There’s where he may have also obtained a handgun, according to authorities.

Read the full story here.

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From Time:

The Navy “did not effectively mitigate access control risks associated with contractor installation access,” at the Navy Yard and other Navy installations, the report by the Department of Defense Inspector General’s office says. Parts of the audit were read to Time by a federal official with access to the document.

The risks resulted from an attempt by Navy officials “to reduce access control costs,” the report finds.

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Navy Vice Admiral Bill French has placed the number of Navy Yard casualties at 27, including 13 dead and 14 wounded. The shooter is among those killed. All 12 people killed by the shooter were civilians, French said.

-- Sabrina Siddiqui

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USA Today reports that at least some of the weapons used in the assault were purchased by Aaron Alexis in Virginia over the last few days.

Read the full story here.

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