It is one of Toronto's longest-lasting and most dangerous gangs, with a history of violence that goes back more than a decade.

And on Tuesday, Toronto Police will outline why they believe the Galloway Boys gang is linked with some of this city's most prominent recent homicides and shootings – including the deaths of two young people at a community barbecue on Danzig Street in Scarborough this summer.

No charges are expected to be laid Tuesday morning.

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Joshua Yasay, 23, and Shyanne Charles, 14, were shot and killed and 23 others were injured when at least two people opened fire at the barbecue on July 16. Police have called the shooting one of the worst in the city's history, and were quick to blame the violence on gang activity.

On Monday night, police announced that they believe the Galloway Boys, a gang whose home base is just one block west of the Danzig house where the shooting occurred, were linked to the deaths of Mr. Yasay and Ms. Charles. They also connected the gang to an eight-month-old homicide nearby, that of 24-year-old D'Mitre Barnaby. He was shot and killed at 3895 Lawrence Ave. East, a five-minute drive west of the Danzig Street shooting.

The gang is also linked to six other shootings that took place in Toronto between Sept. 4, 2011 and Aug. 10, 2012, police said.

"[The police] believe that the three homicides and six other shootings are linked, and that the Galloway gang has an integral part in these events," said Constable Wendy Drummond.

The Galloway Boys are thought to be one of Toronto's larger and better-organized gangs. Their territory is centred around the intersection of Kingston and Galloway Roads, a Scarborough neighbourhood of cheap apartment buildings and social housing in an area built for 1950s families with cars. The lack of transit here is a key barrier to more legitimate business opportunities, community organizers say.

The gang has a long-running feud stretching back decades with the Malvern Crew, a rival gang based in northern Scarborough.

The largest street-gang prosecution in Ontario's history stemmed from that rivalry: Seventeen co-accused faced charges ranging from robbery and weapon possession to first-degree murder in connection with shootings in 2002 and 2004. Prosecutors said the killings caught innocent bystanders mistaken for members of the Malvern Crew. The case involved 17 defence lawyers, eight Crown prosecutors and security measures that were unprecedented at the time.

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In 2009, Tyshan Riley, Phillip Atkins and Jason Wisdom were convicted of first-degree murder, attempted murder and committing murder for the benefit of a criminal organization.

Police believe the recent spate of shootings they say are linked to the Galloway Boys can be attributed to a mix of fighting within the Scarborough gang and external rivalries with members of other gangs, a source told The Globe and Mail. The police source did not point specifically to the Malvern Gang.

"Anytime that you can link nine major crimes like this that's pretty significant," the source said.

Two people have so far been charged in connection with the Danzig shooting: 18-year-old Shaquan Mesquito was charged with uttering threats and several gun-related offences. Police have said they have no evidence suggesting Mr. Mesquito was present when the shooting occurred.

Nahom Tsegazab, 19, was charged with reckless discharge of a firearm. He was among the people injured in the shooting, police have said.

Police have issued several pleas for information on the case, hoping some of the 100 or more people at the Danzig barbecue would come forward as witnesses.

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"We have received some information, granted not enough to lay charges at this point," Constable Drummond said. "It's been some very in depth investigative work that's taken place between the homicide squad and the divisions and [the] guns and gangs [unit] that have been able to link these cases."

Police said they would provide more details about the shootings and homicides Tuesday morning, but do not expect to announce any further arrests or charges.

With a report from Timothy Appleby