The Toronto police officer who shot a teenager on a downtown streetcar two days ago has been suspended from his job with pay, CBC News has learned.

The news about the officer's suspension comes hours after police Chief Bill Blair told reporters that people "have every right to be concerned" after an 18-year-old man armed with a knife on a downtown streetcar was shot repeatedly and killed by police this weekend — an incident captured by amateur video.

Blair said he has seen the video, which was posted online.

"I am very aware that the public is very concerned about this tragic event," he told media in a prepared statement. "They have every right to be concerned."

Witnesses say Sammy Yatim was alone on the 505 Dundas streetcar near Trinity Bellwoods Park when he was shot just after midnight ET Saturday morning. He had pulled a knife and ordered everybody off the streetcar, witnesses say.

The video shows the stopped streetcar at a distance, with multiple police officers nearby, at least one with his hands raised to shoulder height.

Nine gunshots are heard within 13 seconds.

Toronto police Chief Bill Blair says he understands the public has many questions after the shooting on a TTC streetcar. (Nathan Denette/Canadian Press)

Blair said he knows the public has many questions after seeing the video.

"I am also seeking answers to those important questions," he said. He promised an "unwavering commitment" to finding them.

The chief said he has asked Deputy Chief Mike Federico to reach out to the family.

"As a father, I can only imagine their terrible grief and their need for answers," Blair said.

Family mourns

The family, which moved to Toronto from Syria about five years ago, is hiring a lawyer and wonders how police could shoot him multiple times even after it appears he went down.

"He was standing with a knife. Not with a bomb, with a knife," Yatim's mother Sahar Bahadi said.

Bahadi, who has seen the video, said she's heartbroken over the loss of her son, whom she described as polite and gentle.

She said she has many questions about the way the situation was handled by police.

"And I felt that he was very afraid … I felt it. I felt that he was very afraid." Bahadi, a pediatrician from Syria, said she brought her children here because she thought it would be safer, and she had hoped her son would make his future in Canada.

Yatim recently graduated from Brebeuf College School on Steeles Avenue, near Bayview Avenue, CBC's Ivy Cuervo reported.

"He has goals, he has objectives, he works hard," said Ammar Issa, a family friend. Issa said Yatim was working extra hours to try to earn money for college.

A makeshift memorial continues to grow on the spot where the teen was shot.

Police watchdog probing shooting

Blair did not take questions, noting that he is forbidden by law to interfere with the investigation of Ontario's police watchdog, the Special Investigations Unit.

"I regret that I'm unable to answer any of your questions," he said. "The law is rather clear with respect to that."

The SIU has begun an investigation of the incident, as it must under provincial law, and Blair promised to co-operate fully.

SIU investigation Anyone with video footage or other information may contact the SIU's lead investigator at 416-622-1965 or 1-800-787-8529 ext. 1965.

The chief said there will also be an internal investigation. Blair said he is required by law to review the policy, procedures and training of the service, and to see if they were followed.

A full report of the chief's review must go to the police board within 30 days of the SIU's report going to the province's attorney general.

On Monday, the SIU issued a news release updating the public on the status of its investigation into the shooting.

The release said that Yatim sustained "multiple gunshot wounds" in the incident and also indicated that police had also used a stun gun.

The SIU said that it has identified a single subject officer and 22 witness officers.

The Ontario ombudsman also said in a tweet Monday that his office will be "reviewing" the shooting on Tuesday.

Ontario Premier Kathleen Wynne said it was a tragic situation and that her heart went out to the family, but that she couldn't say more given the investigation.

Toronto Police Association president Mike McCormack said the officer involved in the shooting is "devastated."

"He's just overwhelmed by the magnitude of everything," he said. McCormack added that the public shouldn't jump to conclusions before investigators collect all the facts surrounding the shooting.

"All we're asking is wait until all the information comes in, and then we can look at the officer's actions appropriately and make the right diagnosis, as it were," he said.

Security expert concerned

Ross McLean, a security expert and former Toronto police officer, studied a version of the video with enhanced video and audio, frame by frame.

He said it raises serious questions about how police handled the confrontation.

On the enhanced video, a six-second jolt from a Taser can be heard after the gunshots, McLean said. Yatim also appears to put his hands over his head at one point on the enhanced video, he said.

McLean says if the officers had waited another minute for the officer with the Taser to arrive instead of opening fire, Yatim might be alive today. "Should you be Tasering someone who’s been shot six or nine times and lying on the ground?" he told CBC News.

McLean says the video also suggests police did not engage the suspect.

Sammy Yatim was a recent high school graduate. (Facebook)

"Your mouth is your best weapon," he said.

The key is to communicate with and contain the suspect, he said. "He was fairly contained. He was in the streetcar. He could have let that guy sit there all night."

Police can be heard on the enhanced video saying "Drop the knife!" and "If you take one step in this direction, you’re finished," McLean told CBC host Matt Galloway on Toronto's radio program Metro Morning.

McLean said it's unlikely that any of the nine shots were warning shots.

"This officer’s going to have to explain why he used the level of force he did," McLean said.

Vigil held for teen

Martin Baron is a Toronto architect who was on the scene at the time of the shooting. He encountered the incident as he made his way home with his wife and son.

"The whole thing was quick — from the moment we saw the first police officer with the gun to the moment the first shot was fired was maybe 60 seconds," Baron told CBC Radio's As It Happens.

Baron said he could clearly see a "tall skinny kid holding a knife" in the streetcar.

"He looked frozen," Baron said. "Like he was shocked or something."

Police were yelling at the young man in the streetcar, asking that he drop the knife.

"He never did, then they fired their shots," he said.

Baron said he didn't see the young man move, but he noted that he was also looking at other things as the event unfolded.

Baron, who has been interviewed by SIU investigators, said he and his wife have given the video footage they shot to the SIU.

A vigil for Yatim was held. today at Yonge-Dundas Square in downtown Toronto.

Yatim's friends have posted their condolences for the recent high school graduate on social media, and his sister Sarah has started a Facebook group to fight what she considers injustice at the hands of police.