Toronto police say a gang was behind the worst mass shooting in the city's history.

Det-Sgt. Brett Nicol told a news conference Tuesday that investigators have linked the deadly shooting at a June 16 barbecue for young people to the Galloway Boys gang.

Fourteen-year-old Shyanne Charles and 23-year-old Joshua Yasay were killed, and 23 others were sent to the hospital with gunshot wounds.

Det.-Sgt. Peter Trimble says five or six shooters were at the party and that the shootout was related to a confrontation between the Galloway Boys and another neighborhood group.

Trimble says, "We need people to stand up, testify against these people."

Police say they have linked the gang to five other shootings in eastern Toronto between Sept. 4, 2011 and Aug. 10, 2012.