A former co-worker of the Somali refugee CBC News has identified as the man arrested in a weekend attack in Edmonton says Abdulahi Hasan Sharif was an ISIS sympathizer years before Saturday's violent events, and that he had reported him to police.

Terrorism charges are pending against the suspect, who is in custody. Police haven't released Sharif's name, but multiple sources have identified him to CBC.

Sharif's former co-worker, who didn't want to be identified out of concern for his safety, said: "He would rant.

"It was very incoherent. He would just bounce from idea to idea, tangent to tangent, just about what he believed in and he definitely had genocidal beliefs, you could say.

"He had major issues with polytheists. He said they need to die. That sort of thing. I only had a handful of conversations with him about it; those only occurred when there were just two of us in the work room."

Around 8:15 p.m. local time Saturday near Commonwealth Stadium, an Edmonton officer was struck by a Chevrolet Malibu while working crowd control for a CFL game.

Const. Mike Chernyk, standing behind a barricade when he was hit, was sent flying into the air. A man got out of the Malibu and attacked Chernyk with a knife before fleeing on foot.

More than three hours later, a white U-Haul van was pulled over at a checkstop on the city's north side. A police officer recognized the driver's name as similar to the name of the registered owner of the car that had struck the officer earlier.

The U-Haul then sped off toward downtown Edmonton, where streets were filled with Saturday night bar crowds and football fans. Pursued by police, the van struck and injured four pedestrians.

The van tipped over on its side and a suspect was arrested at the scene.

The officer, who sufffered stab wounds to his head and face, has been released from hospital.

One person who was listed in critical condition has been upgraded to stable. Two others have been released from hospital. The fourth victim suffered a fractured skull but has regained consciousness, police said.

The suspect remains in custody, and terror charges are pending, police said. (CBC News)

Edmonton police Chief Rod Knecht confirmed a black ISIS flag was seized from a car where the police officer was attacked.

RCMP said Sunday a 30-year-old Somali refugee was interviewed by the Integrated National Security Enforcement Team (INSET) in 2015.

But there was "insufficient evidence" to make an arrest and the suspect was deemed "not a threat."

Suspect 'strange,' says former co-worker

The former co-worker said he immediately recognized Sharif's name when it began to circulate in the news media.

He worked with a "very strange" Sharif at a construction site in the summer of 2015, he said.

The co-worker said Sharif would play broadcasts in Arabic while they worked at the construction site.

When Sharif started talking to him about his hatred of Shia Muslims and support for well-known leaders of the Islamic State in Iraq and Syria, the co-worker decided he needed to do something, he said.

He said he reported Sharif to Edmonton police, who passed him onto the RCMP. He was later interviewed by RCMP at K Division headquarters near downtown Edmonton, he said.

"They definitely didn't laugh it off … they took it very seriously and very professionally," he said.

Sharif kept a low profile in the city's Somali community.

CBC News conducted numerous interviews with members of Edmonton's Somali and broader Muslim communities, but no one appeared to know Sharif.

The 30-year-old's name triggered no recognition, but Saturday's violence was unanimously condemned.

"This individual has no place in our community," Ahmed (Knowmadic) Ali wrote in a statement Sunday on behalf of the Edmonton Somali community.

"We are your neighbours, co-workers and police officers and we stand strongly beside you in condemning this violence and mourning its effect on the community."

Tactical officers check suspect's apartment

While religious and cultural organizations on Sunday condemned the actions of a man they didn't know, a dozen heavily armed tactical-unit officers used battering rams to enter the rear of an apartment building at 113th Avenue and 117th Street. It's believed Sharif lived in one of the building's suites.

A resident told CBC News that police showed him a picture of a man and that he recognized him as someone he had seen around the building. He didn't know if it was a picture of Sharif.

The officers left about 45 minutes later. Police did not evacuate the building while conducting the search.

Police are expected to provide another update on the case on Monday.