The trial of a court officer accused of assaulting a prisoner started Thursday in London and included defiant and hostile video testimony from the prisoner.

Const. Craig Pickering allegedly assaulted Timothy Van Dusen last May while in a London courthouse cell.

Graphic surveillance video shows the prisoner was injured, but the defence is arguing that reasonable force was used.

Van Dusen was shoved into a wall and blood started flowing onto the floors.

Van Dusen acknowledged in court he has a history of mischief and violence, including assaulting and threatening a peace officer.

“I've had problems with the law my whole life,” he testified. “I get agitated a lot.”

He says he was assaulted just after he made a court appearance on mischief charges.

On May 14, 2013, he threatened to pull the fire alarm at the courthouse.

That's why he was being brought to a special cell, shackled and handcuffed.

The court heard he is very confrontational.

Defence attorney Glen Donald claims Van Dusen was defiant when being restrained and that when Pickering and a cadet tried to put him in his cell, he was unwilling to go.

That’s when Pickering  pushed him in. Van Dusen hit the wall and broke several teeth.

"He struck the far wall. He immediately started to yell, collapsed, and then I saw the blood," said London police Cadet Peter Keane, on the witness stand.

The trial resumes Friday.