EDMONTON — The mother of a young security guard who police believe killed three co-workers and grievously wounded a fourth begged her boy to turn himself in Friday night.

"Please, Travis, I love you and I'm pleading with you with all of my heart to end this without further bloodshed," pleaded Sandy Baumgartner in a statement released by police. "Trav, as your mother, I ask that you come forward now and take responsibility for your actions.

"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."

The mother, who lives with her son in Sherwood Park, on the outskirts of Edmonton, promised the 21-year-old that he is not alone.

"I will be there by your side to support you," she said.

Three armoured car guards were shot to death and another hurt in the wee hours Friday at the University of Alberta. Police believe it was an inside job and have issued a first-degree murder warrant for Travis Baumgartner, who was the fifth member of the crew.

Edmonton police Supt. Bob Hassel said Baumgartner also faces a charge of attempted murder.

"We now believe we have reasonable and probable grounds that this is the person who is responsible for this horrific and terrible crime," Hassel, the head of criminal operations, said Friday.

"We sincerely believe Baumgartner is armed. He's dangerous. And we're urging public to use extreme caution should you happen to encounter this person."

Baumgartner was believed to be driving a Ford F-150 truck. They initially said it had Alberta licence plate ZRE-724. Friday night, they said he has changed the plate to CAA-636. Edmonton police, RCMP, Canada Border Services officials and U.S. Customs agents were all involved in the search.

The guards, employees of G4S Security, were making a delivery to a bank ATM machine in a mall-residence complex on the university campus just after midnight Friday.

Moments later passers-by came upon the ghastly scene. Two guards were found dead by the bank machine with a third critically wounded. The other guard was found dead by a G4S minivan on the street. Baumgartner was nowhere to be found.

A second G4S vehicle, an armoured car, was found hours later parked and idling on the side of the road near an east-end company compound. Police haven't said how, or if, that car was involved.

The dead were Michelle Shegelski, 26, Eddie Rejano, 39, and Brian Ilesic, 35. Matthew Schuman was injured.

Henrietta Shegelski said her son, Victor, married Michelle in April, and the pair were true soulmates.

"Everyone that knew her loved her," she said. "She was just part of our family from the minute we saw her."

Henrietta Shegelski said Michelle worked for G4S for several years. She said Victor is a former soldier who worked with Michelle at the company for a year before going back to school at the University of Alberta.

She said Victor was devastated by the news.

Ilesic's family issued a release to media saying he was deeply loved by his family, friends, and his 12-year-old daughter.

"We are deeply saddened and shocked by today's events and are trying to deal with it as best we can," said the family. "We ask God to take care of him now."

The injured guard, Schuman, is a full-time corporal and Air Force firefighter stationed at Canadian Forces Base Edmonton. He worked with G4S as a second job.

"Our focus right now is on providing support to the family of Cpl. Schuman, who is by his side at the University of Alberta Hospital as he undergoes treatment," Lt.-Col. John Reiffenstein said in a statement.

The shootings occurred at HUB Mall, a long, thin rectangular block of shops, eateries and student apartments on the east end of campus.

One bystander photo of the scene posted to Facebook showed three people from G4S lying in front of the bank machine, emergency crews working over the bodies. There were blood streaks on the floor out from behind the machine to where the bodies were lying.

Ian Breitzke said he saw police pulling out bodies. The 21-year-old accounting student said he was watching TV in his residence room and heard a man in a room behind an ATM crying out in pain.

"When the police came in about 10 minutes, they ended up busting down the door (of the ATM room) and pulling out all the bodies that were in there," he said.

"Another couple of moments after that (they) pulled the man who was still alive out of the room."

The search for Baumgartner included the area around his home in Sherwood Park, on Edmonton's eastern outskirts.

Steven Munz, a friend of Baumgartner's, said his buddy had been with G4S for about three months and had wanted to become a police officer.

"But he felt he really didn't have what it took," Munz said.

He said Baumgartner completed two weeks of training in Calgary before starting the night shift in Edmonton.

"He said he enjoyed it more than any other job."

The pair had been friends since childhood. He said Baumgartner likes to play video games and had worked in the oilpatch and in construction before G4S.

He said he was surprised police think Baumgartner could be involved, but had noticed his personality change in the last year.

"Over the last year I've kind of noticed him slowly changing as a person. It's almost more irrational the way he thinks.

"I didn't think he was capable of something like this, but who knows, right?"

In a profile on the dating website Plenty of Fish, Baumgartner bills himself as an armoured car guard who is into gaming and recreational drug use.

There is a photo of him shirtless in a bathroom holding a cellphone.

He says he's six-foot-four with a laid back personality, a healthy workout regime and a "10" physique.

"I'm a great guy. We don't come around often," he writes.

On his Facebook page, Baumgartner had recently posted some violent quotes from the villainous Joker in the "Dark Knight" movie, which included a violent bank heist.

"You know what I noticed, people don't panic when everything goes (according to plan). If I say a gangbanger or a truck full of soldiers will die tomorrow ... nobody panics. But if I tell them one little old mayor will die ... WELL THEN EVERYONE LOSES THEIR MINDS!!!?!? Introduce a little anarchy."

On June 1, Baumgartner posted the following: "I wonder if I'd make the six o'clock news if I just starting popping people off."

G4S is an international security company with more than 630,000 employees. It has a specialized cash-management arm that delivers pay packets to fill ATMs. Steinberg said the Edmonton office, which has about 100 employees, has limited its operations since the shootings.

Executives from Toronto were flying to Edmonton to meet with staff and police.

"It's devastating," said G4S spokeswoman Robin Steinberg. "Our hearts go out to families of the victims."

Steinberg confirmed the guards were armed, but would say little else.

The university was put in lockdown after the shooting.

Grief counsellors were made available for students living at the HUB residence, and students too traumatized to write exams were being allowed to defer them.

About 560 students are living in residence at the mall at this time of year

A candlelight vigil was to be held Friday night and flags at the university were lowered to half-mast.

Curt Binns, executive director of the ATM Industry Association Canada in Toronto, said the amount of money put into bank machines at any one time varies widely.

"I worked at a branch of a bank right downtown and on weekends, when there would be things like the Carribana Festival or the gay (pride) parade, and a baseball game at the same time, we would put about $110,000 in the machine," he said.

"That's downtown Toronto where you have millions of foot traffic on a particular weekend. But if you're in (a town), population 500, and there's nothing happening on the weekend, the operator might put $1,000 in the machine."

It was the second robbery of a G4S armoured vehicle in Edmonton in recent months. Last December, guards making a mid-afternoon pickup outside a casino were attacked and pepper-sprayed by two masked men. The pair fled in a Jeep with an undisclosed amount of money. No arrests have been made.

In Calgary, two men dressed in military fatigues and armed with assault rifles and tear gas ambushed two Brinks guards delivering $300,000 in cash to a north-end mall in 1998.

More than 80 bullets were exchanged in a fierce gun battle, but no one was hurt. The robbers fled empty-handed and were later arrested.