Travis Brandon Baumgartner, 21, is shown in a police photo released on Friday June 15, 2012. THE CANADIAN PRESS/HO

EDMONTON - Police in Edmonton are hunting a man they believe is a "dangerous" killer, brazen enough to gun down four of his armoured-car guard colleagues, leaving three of them to die on the grounds of the University of Alberta.

Travis Baumgartner was still at large after the shooting, which happened in the wee hours of Friday morning as he and his G4S Security crew were re-stocking a bank machine on the ground floor of one of the school's residences.

Police are calling what happened an armed robbery, but there has been no confirmation that any money was taken. An abandoned armoured car was later found halfway across town near a G4S office with its lights on and its motor running.

The 21-year-old Baumgartner is being sought on warrants for three counts of first-degree murder and one of attempted murder.

Late Friday night, the fourth guard who was shot was still fighting for his life in an Edmonton hospital with critical injuries.

Baumgartner's mother made a plea to her son late Friday to turn himself in. She alluded to a fight the two had before the shooting and apologized to her son.

"I'm sorry that we had an argument last night and that we had bad words between us, but I want you to come home and do the right thing. Let's work this out together," she said in a statement read by police.

Friends say Baumgartner had designs on being a police officer, but settled into a job with G4S instead after deciding he didn't have what it takes for law enforcement.

He likes video games and calls himself a recreational drug user.

In an online dating profile, he says he is a "great guy" who is laid back and has a "10" physique.

But his Facebook page is much darker, quoting the anarchist Joker from the movie "Dark Knight" and musing about "popping people off."

While police look for Baumgartner, details are emerging about the colleagues he is alleged to have left bleeding on the ground at the university.

Michelle Shegelski was 26 and had just gotten married to her husband, Victor, a former military man who, coincidentally, had just returned to school at the University of Alberta. Eddie Rejano, 39, and Brian Ilesic, 35, were the other two guards killed.

The injured guard was identified as Matthew Schuman. G4S was his second job. He was a full-time corporal and Air Force firefighter stationed at Canadian Forces Base Edmonton.

A Facebook group popped up Friday night as a tribute to all four.

"My thoughts and prayers for the families and co-workers for their loss," one poster wrote.

"So sad."

News from © The Canadian Press, 2012