TORONTO - A snub at a summer barbecue sparked a "violent confrontation" between two rival gangs and what's been called the worst mass shooting in Toronto's history, police said Thursday in announcing murder charges.

The clash at the July 16 block party on Danzig Street left Shyanne Charles, 14, and Joshua Yasay, 23 — who police have said were innocent partygoers — dead and more than 20 others wounded.

Members of the Galloway Boys, a local street gang, were at the barbecue and "took ownership" of it, said Staff Insp. Greg McLane.

A member of another gang, the Malvern Crew, showed up at the party but was turned away, McLane said.

"It's alleged that the Malvern Crew member left the barbecue, called a number of his associate gang members and attended back at the barbecue to confront the members of the Galloway Boys to seek revenge for being turned away," he said at a news conference.

"This resulted in a violent confrontation between a number of gang members from the Galloway Boys and from the Malvern Crew that involved a number of firearms."

Police announced Thursday that Shaquan "Bam Bam" Mesquito, 18, has been charged with two counts of first-degree murder, attempted murder, reckless discharge of a firearm and 23 counts of aggravated assault.

The first murder charges in the shooting are a milestone in the investigation, said Toronto Police Chief Bill Blair, but he called more arrests "inevitable."

"There are others who also bear a responsibility for what took place in the Danzig community on July 16 and we're going to hold them to account," he said.

Mesquito faces two counts of first-degree murder, but it doesn't mean police necessarily allege he fired the shots that killed Charles and Yasay.

"I'm not saying that he's solely responsible for all the carnage that happened that day," McLane said.

Police likened the scenario to a shootout on Boxing Day 2005 in Toronto that killed 15-year-old Jane Creba.

Gunfire erupted as two rival groups of young men confronted each other on Yonge Street. Police were unable to determine whose gun actually fired the shot that killed Creba, but several people were convicted of murder and manslaughter charges.

The courts held that all those convicted in Creba's case were participating in a reckless activity likely to injure or kill someone and therefore bear responsibility for her death.

Mesquito has already been in jail since shortly after the shooting, facing a charge of threatening to cause serious bodily harm also related to the barbecue. He appeared in court Wednesday on the new charges and was remanded into custody.

Police also released composite sketches of two people of interest. They are both described as black men in their 20s, one with a scar under his left eye. McLane said it's not yet known if they were involved or were just witnesses, but police would like to speak with them.

Another suspect in the incident, Nahom Tsegazab, 19, was charged earlier this year with reckless discharge of a firearm.

Police have said the Galloway Boys have been linked to at least five other shootings in the past year and they are aware of conflicts between them and the Malvern Crew.

Blair described the gangs' strength as "significantly diminished," but McLane noted that others wait in the wings, ready to take up the mantle.

"My understanding is that the Malvern Crew and the Galloway Boys are in a period of transition because of some significant arrests that were made historically," he said.

"There are people that will always try to take up the void in these gangs and make themselves known to other members of the community."

Blair said he understands community members' fear of coming forward to police with information and tried to provide assurances that police will deal with their tips sensitively.

"We will provide all of the support to individuals who do come forward because we need their help and they need our support," he said.

"We need people to step forward and tell us what they know."

Note to readers: This is a corrected story. Information initially provided by police said Mesquito faced 24 charges of aggravated assault.

Earlier on HuffPost:

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  • Shyanne Charles, 14, was killed in the shooting on Scarborough's Danzig Street.

  • Police interview neighbours on Tuesday July 17, 2012 near the scene of a shooting on Danzig Street where 19 people were injured and 2 confirmed dead at an outdoor barbecue that took place on Monday July 16, 2012.

  • Neighbours watch on as police walk by on Tuesday July 17, 2012 near the scene of a shooting on Danzig Street where 19 people were injured and 2 confirmed dead at an outdoor barbecue that took place on Monday July 16, 2012 .

  • Mayor Rob Ford speaks to media after visiting the scene of Monday night's shooting on Danzig St. in Toronto on Tuesday July 17, 2012. Toronto police are calling for witnesses to come forward following a deadly shooting at an outdoor neighbourhood party that left two people dead and sent 21 others to hospital, including an infant, in what police are calling the worst incident of gun violence in the city's recent history.THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Mayor Rob Ford (right) visits the scene of Monday night's shooting on Danzig St. in Toronto on Tuesday July 17, 2012. Toronto police are calling for witnesses to come forward following a deadly shooting at an outdoor neighbourhood party that left two people dead and sent 21 others to hospital, including an infant, in what police are calling the worst incident of gun violence in the city's recent history.THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Shyanne Charles, 14, was killed in the shooting on Scarborough's Danzig Street.

  • Joshua Yasay, 23, was killed in the shooting.

  • Shyanne Charles, 14, was killed in the shooting on Scarborough's Danzig Street.

  • Police interview neighbors near the scene of a shooting in Toronto, on Tuesday, July 17, 2012. Two people are dead and 19 were injured as gunfire broke out late Monday night as more than 200 people attended an outdoor community barbecue. Police described the shootout, which involved multiple guns, as an "unprecedented" episode of violence. (AP Photo/The Canadian Press,Aaron Vincent Elkaim )

  • Toronto Police Chief Bill Blair arrives for a news conference on Monday night's fatal shooting at a street party in Scarborough, in Toronto, Tuesday, July 17, 2012. THE CANADIAN PRESS/Ian Willms

  • Police interview neighbors near the scene of a shooting in Toronto, on Tuesday, July 17, 2012. Two people are dead and 19 were injured as gunfire broke out late Monday night as more than 200 people attended an outdoor community barbecue. Police described the shootout, which involved multiple guns, as an "unprecedented" episode of violence. (AP Photo/The Canadian Press,Aaron Vincent Elkaim )

  • Shannon Longshaw;

  • Police stand on guard on Tuesday July 17, 2012 on Danzig Street near the scene of a shooting where 19 people were injured and 2 confirmed dead at an outdoor barbecue that took place on Monday July 16, 2012 . THE CANADIAN PRESS/Aaron Vincent Elkaim

  • A police officer places a marker on Danzig Street in Toronto on Tuesday, July 17, 2012 near the scene of Monday night's shooting. Toronto police are calling for witnesses to come forward following a deadly shooting at an outdoor neighbourhood party that left two people dead and sent 21 others to hospital, including an infant, in what police are calling the worst incident of gun violence in the city's recent history. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Pedestrians look on near the scene of a shooting in Toronto early Tuesday, July 17, 2012, that left 19 people injured and two dead at a house party late Monday July 16. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Toronto Police Chief Bill Blair speaks to the media in Toronto early Tuesday, July 17, 2012, near the scene of a shooting that left 19 people injured and two dead at a house party late Monday, July 16. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Toronto Police Chief Bill Blair walks down Morningside Ave in Toronto early Tuesday, July 17, 2012, following a shooting that left 19 people injured and two dead at a house party late Monday, July 16. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Police stand on guard on Morningside Ave. in Toronto early Tuesday, July 17, 2012, near the scene of a shooting where 19 people were injured and two dead at a house party late Monday, July 16. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • Toronto Police Chief Bill Blair speaks to media in Toronto early Tuesday, July 17, 2012, near the scene of a shooting where 19 people were injured and two were left dead at a house party late Monday July 16. THE CANADIAN PRESS/Aaron Vincent Elkaim

  • A man is attended to on the scene and loaded onto a gurney for transport following a shooting that left 19 injured and two dead in Toronto late Monday, July 16, 2012. THE CANADIAN PRESS/Toronto Star - Rick Madonik

  • ETF officers stand guard following a shooting that left 19 injured and two dead in Toronto late Monday, July 16, 2012. THE CANADIAN PRESS/Toronto Star - Rick Madonik