Fellow inmate Mitch Cutknife told reporters Thursday that Jeff Oatway was handcuffed and restrained on the floor when police zapped him at their downtown Edmonton headquarters on April 11.
Cutknife admitted he did not actually see police fire the electronic stun gun, but believes officers had no reason to use it in the first place.
"He wasn't harming anybody while he was handcuffed," said Cutknife, 30, who is from Hobbema, Alta. "That wasn't right."
Oatway, 34, was in a coma on life support and died two days later. Cutknife said he decided to go public when he found out about the death. He also filed a complaint of excessive force with the police chief.
Police have said Oatway had to be Tasered during a struggle with officers in a detainee management unit. They said he became violent in an office, turned over desks and smashed computers. About a dozen officers were called in to help.
Cutknife said he heard a commotion and soon after saw officers drag Oatway in handcuffs down the hallway. They went around a corner so he didn't see clearly what happened next.
But he said he heard one officer talk about taking "the claws out." Cutknife then heard screaming.
Police said the man suffered a "medical episode" and an ambulance was called.
Oatway's parents have said he was mentally ill and could have become violent, but they wish police had found some other way to control him.
Edmonton homicide detectives are investigating the death under the supervision of the Alberta Serious Incident Response Team, which reviews deaths or serious injuries involving police.
ASIRT's executive director, Clif Purvis, said investigators have secured surveillance videotapes from the cells area and are interviewing witnesses.
"We will take all the steps to make sure that we accurately figure out what happened and when it happened," he said.
Sgt. Tony Simioni, president of the Edmonton Police Association, said he stands by his earlier statement that Oatway was Tasered during a confrontation with officers. He said the video will show what happened.
Defence lawyer Tom Engel, who helped Cutknife file his police complaint, said a fatality inquiry will also go over what happened.
Tasers have been linked to the deaths of more than 25 people in Canada. The U.S. company that makes them says they have never directly been proven to have caused a death in Canada.