Prosecutors argued Tuesday that a retired Quebec judge charged with first-degree murder killed his wife because he was planning to start a new life with his mistress.

The Crown opened its case against former Quebec Superior Court Justice Jacques Delisle Tuesday. Jury selection was completed on Monday.

Delisle, 77, is accused of killing his 71-year-old wife, Marie-Nicole Rainville, who was found shot to death inside the couple's Quebec City condo in November 2009.

Rainville was partially paralyzed after suffering a stroke, and was also recovering from a broken ankle, reported CTV Montreal's Stephane Giroux. Delisle had retired earlier that year.

Delisle told police his wife had shot herself, and at first her death was listed as a suicide. Seven months later, Delisle was charged.

"At first it did look like a suicide," Giroux said outside court Tuesday. "The former judge had called 911 to say he and his wife had an argument that morning, he went out to run some errands and came back to see his wife sitting in a chair, dead, a gunshot wound to the head and plenty of blood."

The 911 call was played for the jury during Tuesday's proceedings. Delisle claimed his wife used his gun, which he had stored in a wooden box in their home.

Also Tuesday, police investigator Denis Turcotte took the stand, and said the suicide story seemed odd, given that gunpowder residue was found on the palm of Rainville's hand. Residue is usually found on the outside of a shooter's hand.

Upon further investigation, police learned that Delisle had a mistress, his former secretary, with whom he was allegedly planning to move in.

"So (the prosecution's) theory right now is the judge shot his wife to get rid of her because she had become a burden for him in his new life," Giroux said.

Delisle's former secretary is expected to take the stand.

The case is believed to be the first time a Canadian judge is facing a first-degree murder charge. Delisle is also charged with possessing an illegal firearm.

With a report from CTV Montreal's Stephane Giroux and files from The Canadian Press