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Kimveer Gill is shown in an undated photo taken from a website. ((Canadian Press))

The gunman whokilled an 18-year-old student in a shooting rampage at Montreal's Dawson College on Wednesday died of a self-inflicted wound, said a spokeswoman with la Sûreté du Québec late Thursday afternoon.

Preliminary autopsy resultsperformed on the body of 25-year-old Kimveer Gill confirm he sustained two bullet wounds during a shootout with police: one in the arm, probably from a police officer's gun, and the other a self-inflicted shot to the head, said Chantal Mackels. Ballistic tests are being carried out on the first bullet to confirm it came from a police officer's gun.

The revelation is a major step forward in the police investigation into the eventssurrounding the deadly attack at thecollege.

Montreal police continued to interview hundreds of eyewitnesses Thursday as they piece together a timeline to explain what happened at Dawson College.

Anastasia De Sousa was killedand 19 people were injured before Gill, a self-described loner from Fabreville, turned the gun on himself, said police.

Quebec's provincial police took over theinvestigation intothe gunman's death because Montreal police officers were involved. Montreal police are leading the main investigation.

Investigators search for clues

The college remained cordoned off with police tape on Thursday as forensic investigators went over the site in search of evidence.

Early Thursday morning, they removed the body of De Sousa, who was shot dead inside the school.

Police say they knew the young woman was dead early Wednesday afternoon, but did not confirm that information until much later to avoid spreading panic, said spokesman Yan Lafrenière.

Police have already met with 100 witnesses and planned to meet with 200 more Thursday, said Lafrenière.

Investigators have a monumental task ahead of them because of the number of people who were inside or near the college when Gill, dressed in black from head to toe, started shooting randomly at people just before 1 p.m. on Wednesday.

"There's so much information," said Lafrenière, commenting on rumours that swirled among witnesses and media outlets. He said police have been sifting through those accounts and now have a clearer picture of what happened.

Police are certain there was only one gunman involved in the shooting, Lafrenière told CBC News.

"[On Wednesday] people were mentioning there were shots fired at different locations. That wasn't true but, because of the state of shock and the cellphones, people were calling from different locations," he said.

Police now believe that shots were only fired in and around Dawson College, he added.

Armed with three weapons

Gill is believed to have been carrying at least three weapons: a handgun, a 12-gauge shotgun and a semi-automatic or automatic rifle. SQ investigators searched his car late Wednesday night.

"We know he took the car to come to Dawson College, so we're trying to understand exactly what was in the car: more firearms, notes or pieces of paper," said SQ spokesman François Doré.

There had been conflicting reports about how Gill died. On Wednesday, Delorme said Gill had been shot dead by officers. Later, police said they were waiting for results fromthe autopsy.

Investigators also met with Gill's parents at their home in Fabreville, a borough in Laval, north of Montreal, where they confirmed the young man's identity and car. Gill was not previously known to police and his parentswere shocked, said Doré.