A spate of killings and shootings in Toronto's east end are tied to a leadership vacuum inside one of the city's most notorious gangs, police say. And the worst mass shooting ever in Toronto's history is linked to that same gang.

On Tuesday morning, at a news conference in a parking lot where one of the killings happened, police said they have evidence that links three homicides and a series of shootings to the gang known as the Galloway Boys.

"We have some information that the shooters in these incidents are vying for the leadership within the Galloway Boys group," said Det.-Sgt. Brett Nicol, who is leading the investigation into one of the slayings.

D'Mitre Barnaby was shot and killed by mistake, police say. (CBC)

"These guys are involved in all sorts of criminality from drug dealing, weapons trafficking and prostitution," he said.

Police also revealed that the shooting death of D'Mitre Barnaby was a tragic case of mistaken identity.

Barnaby was found shot to death outside an apartment building on Dec. 30, 2011, just a few blocks from where the street party took place.

No charges have been laid in that slaying.

Police now say they believe Barnaby was the victim of mistaken identity: that the Galloway Boys mistook him for the real target.

According to Nicol there was an "amazing" resemblance between Barnaby and the intended victim who also lives in the neighbourhood. Police did not identify the intended target.

In the case of the slaying of Barnaby, police believe the Galloway Boys were trying to settle a score with another group known as the Orton Park Boys.

Police also provided a video compilation of the circumstances surrounding Barnaby's slaying.

Danzig Street shootout

The other two deaths linked to the gang took place during a street party near to the home base of the gang.

There was a wild shootout at a street party on Danzig Street that left a 14-year-old girl and a 23-year-old man dead.

In the street party shooting — the worst mass shooting ever in Canada's largest city — Shyanne Charles, 14, was killed along with Joshua Yasay, 23. Both were innocent bystanders who were just taking part in the July 16 street festival.

Twenty-three others were taken to hospital.

On Tuesday, police made a renewed appeal for witnesses, but at the same time gave the first real explanation for the reason behind the shootout: a turf battle.

Det.-Sgt. Peter Trimble said the wild night of violence started after one of the Galloway Boys tweeted that he was hosting the block party and was giving out free Hennessey cognac.

The tweet drew people from other parts of Scarborough, and Durham region, including some from the Malvern area, though Trimble said he didn't believe those people were members of the Malvern Crew.

The Malvern Crew is another Scarborough gang that is based north of the Galloway Boys.

Those who arrived from Malvern were confronted by the Galloway Boys who told them to leave. They did, but returned with more people and that's what led to the shootout, Trimble said.

Police now believe there were five or six shooters who let fly into the crowd of more than 100 people.

Trimble appealed for witnesses to come forward but admitted police are even having problems gathering statements.

"Some of the victims have not been co-operative," he said.

Police have recovered 25 shells and five firearms.

Two people have been charged in the wake of the Danzig Street shootings: Nahom Tsegazab, 19, with reckless discharge of a firearm and Shaquan Mesquito with uttering threats and several other gun-related charges. Police do not believe Mesquito was at the street party when the shooting erupted.

Tsegazab was described Tuesday as a Galloway Boys gang member. Trimble said his street name is "Gifted."

Forensic evidence also links the Galloway Boys to six other shootings that took place in Toronto between Sept. 4, 2011 and Aug. 10, 2012, police said.

The Galloway Boys — and their rivals the Malvern Crew — have been targeted at different times by police in an effort to smash the city's gangs and reduce the escalating violence in Toronto's Scarborough neighbourhood.

The previous investigations have led to arrests, charges and convictions but Nicol said Tuesday that many of the gang members have now passed through the justice system and are back on the streets.

Some of the older gang members are now acting as "mentors" to the younger recruits, he said.

Toronto Star reporter Betsy Powell wrote a book on the Galloway Boys that was published two years ago.

Back when she wrote the book, Powell quoted a gang member who was caught on a wiretap saying that “the next generation is coming up” in the streets.

"I think that is what is playing out today," Powell told CBC News in an interview on Tuesday.

With a report from the CBC's John Lancaster