A convicted Canadian contract killer confessed to 28 murders and 12 attempted murders over the course of three decades, at his trial in Quebec.

Gerald Gallant's victims included bikers and alleged members of organised crime groups, as well as bystanders who were not intended to be targets, the BBC reported Wednesday.

Already serving life for a 2001 murder, he pleaded guilty to a further 27.

Gallant, 58, was caught in 2006 after fleeing to Europe when detectives linked him to that killing. Having turned police informer, he will not get additional jail time for his other crimes and is eligible to apply for parole in 25 years.

Under his plea deal, he is barred from writing a book or making a film about his crimes but prosecutors said he would receive protection and would be given USD 50 a month to spend at the prison canteen.

Quebec has been wracked by drug-related turf wars between motorcyclist gangs.

Gallant's unintentional victims included a waitress he wounded in 2000 while killing Robert Savard, an associate of the Hells Angels motorcycle gang, who was using her as a human shield.

In 1999, he mistakenly shot dead a private detective living in an apartment formerly occupied by his intended target.

Gallant apologised before survivors and relatives of his victims in court on Tuesday.

"I regret the hurt I have caused the victims and their families," he said.

Acting on information provided by the killer, police arrested 10 people across Quebec last week in connection with dozens of biker-related murders.