The United States is in the iron grip of a miserable week in what has often been a cruel month for Americans: April, during which several similarly traumatic events have shaken the nation to its core over the past 20 years.
A few hours after U.S. President Barack Obama delivered a rousing address Thursday at an interfaith service in Boston to honour the victims of the marathon bombings, federal investigators revealed they have two male suspects in their sights in the attack.
The FBI appealed to the public for information on two "armed and dangerous" suspects shown on surveillance camera video released on Thursday.
Both young men, each wearing baseball caps, are seen in the video hauling large knapsacks shortly before the blasts. One of them is seen putting down his backpack at the site of the second blast in Monday's attack; both are seen making their way through the crowd together.
"Somebody out there knows these individuals … though it may be difficult, the nation is counting on those with information to come forward and provide it to us," Richard DesLauriers, a Boston FBI official, told a news conference.
"We consider them to be armed and extremely dangerous. No one should approach them," he added. "If you see these men, contact law enforcement."
Within hours of his appeal, NBC reported, citizens were calling in with names.
Bloomberg reported late Thursday that Jeff Bauman, who lost both legs in the blast and was the subject of a harrowing photograph as he was being wheeled to paramedics, woke up from surgery to tell investigators he'd witnessed a man drop a bag at his feet shortly before the blast.
"He woke up under so much drugs, asked for a paper and pen and wrote, 'bag, saw the guy, looked right at me,'" Bauman's brother, Chris, told Bloomberg in an interview.
In Texas, meantime, investigators were trying to determine whether a fire and subsequent mammoth explosion at a fertilizer company on Wednesday night was accidental or criminal in nature.
The tiny town of West, just up the road from Waco, has been devastated by the blast, but officials were refusing to provide a death toll estimate at a scene likened by some officials to a nuclear fallout zone. More than 160 people were injured.
The blast all but levelled a five- to six-block radius surrounding the plant, where two massive tanks contained highly pressurized anhydrous ammonia. As many as five firefighters are among those missing.
The explosion occurred almost exactly 20 years after the 50-day siege in Waco ended disastrously in 1993 with the deaths of 83 cult members. Federal agents, suspecting firearms violations, were trying to force them out of their Branch Davidian compound when a fire broke out.
Indeed, this week marks the anniversaries of Waco (April 19, 1993), the Oklahoma City bombing (April 19, 1995), the Columbine high school massacre (April 20, 1999) and the Virginia Tech mass shootings (April 17, 2007).
Timothy McVeigh, the right-wing extremist behind the Oklahoma City blast, timed his deadly attack to coincide with the second anniversary of Waco. Until Sept. 11, 2001, it was the most destructive act of terrorism on American soil in U.S. history, killing 168 people, including 19 children under the age of six.
In Texas on Thursday, rescue crews were trudging through the smouldering ruins of West, looking for survivors. More than 160 were injured in the explosion that destroyed dozens of houses, businesses, at least one apartment complex and a nursing home.
"I don’t know how many folks may still be trapped in rubble," Waco police Sgt. William Patrick Swanton told reporters on the scene. "Homes have been destroyed. There are homes flattened. Part of that community is gone."
Initial evidence suggested the explosion might have been an industrial accident. The Associated Press reported Thursday that federal regulators fined the West Fertilizer Co. $10,000 last summer for safety violations. The company paid $5,250 after taking what it described as corrective actions.
A Mississippi man, meantime, appeared in court charged with mailing poison-laced letters to U.S. President Barack Obama, a Republican senator and a Mississippi judge. Paul Kevin Curtis, 45, clad in a Johnny Cash T-shirt, made an appearance in a federal courtroom in Oxford, Miss., on Thursday morning.
The Elvis impersonator's lawyer says her client insists he's innocent of the charges.
"I know Kevin, I know his family," said Christi McCoy. "This is a huge shock."
The FBI says the letters, laced with ricin, read:
"No one wanted to listen to me before. There are still 'Missing Pieces.' Maybe I have your attention now even if that means someone must die. This must stop. To see a wrong and not expose it, is to become a silent partner to its continuance. I am KC and I approve this message."
The FBI's affidavit says Curtis had sent letters to Wicker's office several times previously with the message: "This is Kevin Curtis and I approve this message." He also wrote of a novel he was working on about the sale of human body parts entitled "Missing Pieces."
In a rare moment of levity this week, Wicker said not only had he met Curtis, but he'd hired him about 10 years ago to perform as Elvis at a party.
"I have indeed met him," he told reporters on Capitol Hill. "He was very entertaining. He was more stable then."
As he's done so many times during his five years in office, Obama once again took on the role of comforter-in-chief on Thursday in Boston.
"We may be momentarily knocked off our feet," the president said during the service at a downtown cathedral. "But we'll pick ourselves up. We'll keep going. We will finish the race."
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