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The blast site is shown here in an aerial shot Monday afternoon.

Homicide detectives have taken over the investigation into a massive explosion that killed four people and destroyed two houses in north Edmonton Sunday.

"The deaths are being treated as suspicious," acting police chief Darryl da Costa told reporters Monday. The deaths are being treated as suspicious in nature as a matter of procedure because they are still unexplained, he said.

The blast was not caused by an explosive device or a drug lab, da Costa said, adding the investigation is still ongoing.

Police announced Monday that the body of a fourth victim — a woman — was found in the debris, a day after Edmonton Fire Rescue confirmed three men had died in the blast.

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Brad Winter, 26, was killed in Sunday's blast. ((Facebook))

"It may take days or weeks to pinpoint the cause," da Costa said.

The four people died when a house at 91st Street and 180A Avenue exploded at about 1:20 p.m. MT.

According to land titles, the house is owned by Dwayne Poirier and Jeanne Cathleen Heard. Their whereabouts at the time of the explosion are not known.

Friends have identified Brad Winter, 26, and Craig Huber, 30, as two of the victims. The two men lived next door to the house that exploded. A woman and three-year-old boy escaped from the same house.

Huber's aunt, Deanna Vodden, read a statement Monday afternoon on behalf of the family.

"We have suffered a great loss and, at this time, we would like our privacy to deal with this tragedy," she said. "We appreciate all the support and messages that we have received."

Autopsies are scheduled to take place on Tuesday.

About 40 people forced to leave homes

Twenty-eight homes were damaged by the blast, forcing about 40 people to leave their homes, an emergency official said.

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Craig Huber, 30, was also killed in Sunday's blast. ((Facebook))

The explosion shattered windows in nearby homes, and pieces of wood, broken glass and tree branches littered the streets. The area was blocked off on Monday and some residents were only allowed back into their homes to grab some personal items late Monday afternoon.

Marg Whyte had just returned home from a trip to British Columbia around the time the blast occurred.

While police told her damage to her house was minor, she hadn't yet seen it herself.

"It's been rough. I didn't sleep last night. I stayed at a friend's place," Whyte said. "I was here at five this morning. I got kicked out and now I'm back and I have to go to work. I have no clothes, nothing."

Rita Carrothers was away from her house when the explosion took place. Like Whyte, she hadn't seen her house and wasn't sure about the extent of the damage. She stayed at her daughter's place Sunday night and was wearing her daughter's clothes on Monday.

"I was just scared and hoping that my house would be OK and that everybody else's around me would be too," she said.

People will not be allowed to move back into their homes until the structures are deemed safe by inspection teams.

"It's very important that people realize that we're going to be very diligent in ensuring that their homes are safe and they get back to them as soon as possible," Mayor Stephen Mandel said.

Neighbours heard a big bang

Mathieu Comeault, 18, was across the street in his house when the explosion happened. Comeault told CBC News he heard a big bang and ran out into the street to see what had happened.

"I saw my neighbours and they said that a house had exploded," Comeault said. "I ran inside and grabbed my shoes and got there as fast as I could."

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Workers clean up after an explosion destroyed two homes in northeast Edmonton on Sunday. Three men and a woman were killed.

Several people had gathered at the scene to try to help people, said Comeault, who helped pull a woman and her son out of one of the homes.

"There was a bunch of us out there, and we kind of just handed them down the line and got them out to the street as fast as we could," he said. "There was a lot of people who helped."

Phil Stagg heard the blast from several blocks away.

"I got there and there was an old lady coming out of the house next door, and she was all cut up with glass," Stagg said. "The house was basically gone.

"You could see right into the basement, just a pile of rubble, half the house next door was gone."

On Sunday, hazardous materials crews swept the area and no unnatural chemicals were detected. Officials set up a decontamination site on scene where crew members were rinsed off as they left.

With files from The Canadian Press