06/01/2012 06:55 EDT | Updated 08/01/2012 05:12 EDT

More witnesses sought in fatal Vancouver police shooting after release of video

VANCOUVER - An Alberta agency investigating a fatal police shooting in Vancouver is looking for more witnesses to the incident following the release of a video of the killing.

After the video emerged this week, the B.C. government asked the Alberta Serious Incident Response Team to review the case, in which Paul Boyd was fatally shot by police in August 2007.

The officer who fired the fatal shot, Lee Chipperfield, testified he thought Boyd was armed, but the video shows an apparently unarmed man crawling on his hands and knees seconds before he is killed.

The Alberta team says it's spoken to the person who provided the video but there may be other witnesses who didn't speak to Vancouver police at the time of the shooting and it's asking them to come forward now.

At a news conference Thursday, Vancouver Police Chief Jim Chu said 12 witnesses were interviewed after the shooting but police didn't know anyone had videotaped the incident.

Chu also apologized to Boyd's family, but his sister, Deborah Boyd, said various apologies were nothing more than excuses for an officer who should have been disciplined for firing multiple shots at her mentally ill brother.

A March 2012 report by the Office of the Police Complaint Commission said two plainclothes officers first arrived on the scene after receiving 911 calls about a disturbance. They were followed by two uniformed constables, including Chipperfield.

The report said police encountered Boyd as he sat on a bench talking to another man and appeared calm.

However, when one of the officers approached Boyd, the officer reported Boyd appeared to be trying to conceal a hammer.

The report said at that point, the officer drew his gun and ordered Boyd on the ground. When an officer approached, trying to handcuff him, "Boyd jumped up, wielding a bike chain and lock" and struck the officer on the side of the head, knocking him to the ground, the report said.

A second officer was also struck by the chain, the report said, adding Boyd ran into the middle of the street where he continued to swing the chain.

It said when Boyd approached Chipperfield and two others in an aggressive manner, Chipperfield began firing the first of what would be nine shots, with the final one fired into Boyd's head, killing him.