The Canadian press has depicted Gill as obsessed with weapons, violent video games and the Goth subculture.
Montreal police chief Yvan Delorme confirmed to Radio-Canada that it was Gill, a Montreal native of Indian origin, who entered Dawson College and started shooting at students.
Gill killed a woman and wounded 19 people before police shot him dead.
Earlier Canadian media had identified Gill It was also reported that he had threatened violence on his website.
He wrote in his blog that he hated humanity and wanted to die "under a hail of bullets," media outlets reported.
Mr Delorme has criticised the media for quickly revealing Gill’s identity and details about his life.
"It isn't necessarily helpful for an investigation to prematurely advise the family and go looking on the website," Delorme said in an interview with Radio-Canada.
Several newspapers published photos, obtained from his website, of a young man wearing a Mohawk hairstyle, dressed in black and brandishing a gun or commando knife.
In the last photo on the website, Gill appears dressed in a black trench coat and carrying an automatic weapon with a text that read "ready for action," the French-language daily La Presse reported.
“Turn this world into a cemetery. Crush anyone who gets in the way. Leave a river of blood on your way. Leave a river of blood in your wake," La Presse quoted him as writing.
Blog reveals anger
According to La Presse, on the morning of the rampage, Gill made a new entry in his blog, asking readers to listen to a song by heavy-metal group Megadeth, whose refrain proclaims in French and English:
"A Tout Le Monde (to everyone)
"A tout mes amis (to all my friends)
"Je vous aime (I love you)
"Je dois partir (I must leave)
"These are the last words
"I'll ever speak
"And they'll set me free"
To a question posted on the website asking how Gill wanted to die, he wrote "like Romeo and Juliet or in a hail of bullets," La Presse reported.
Gill often raved about guns and against society. "Society disgusts me. It's the fault of everyone who does nothing unless it concerns them personally. (Expletive) you society," the newspaper quoted him as writing.
Mr Delorme said Wednesday there were no indications the shooting was an act of terrorism or motivated by racism. He said the gunman acted alone.
Critical condition
Tarek Razek, head of the traumatology departement at Montreal General Hospital said on Thursday, two of the 19 hit by gunfire were in extremely critical condition.
Eleven of the wounded six men and five women aged 17 to 48, were taken to the hospital, Dr Razek said.
Canadian Prime Minister Stephen Harper called the shooting shocking and incomprehensible as the new details about it emerged.
"This is a shocking and appalling tragedy," Mr Harper said.
"How do you explain somebody who wants to end their life and wants to end it by killing other people, other people they don't know, just for the sake of killing them? It's impossible to explain and comprehend," Mr Harper said.
The shooting recalled the so-called Montreal Massacre on December 6, 1989, at Montreal's engineering school Ecole Polytechnique.
In that incident, a gunman, Marc Lepine, killed 14 female students before killing himself.
And in August 1992 a professor at Concordia University in Montreal killed four colleagues.
Website link
A website used by Gill has surfaced in other violent Canadian incidents including one in which an Alberta girl allegedly killed her family in April, news agencies Reuters and AAP reported.
The www.vampirefreaks.com website is described by its New York-based founder as a goth/industrial site.
Gill posted photographs and comments on the site and said he loved guns and hated people.
Jesse Hirsh, president of technology services firm Openflows Networks Ltd in Toronto has said it's not the first time the website has been in the news.
In a Toronto trial last year the girlfriend of a youth accused of killing his younger brother and attempting to kill his stepfather was revealed to have had a profile and pictures on the site.
And a 23-year old man and his 12-year-old girlfriend accused of killing a woman, her husband and their eight-year-old son in Alberta last April also reportedly had profiles on vampirefreaks.com.