A defence lawyer at the Quebec City murder trial for retired judge Jacques Delisle is raising doubts about the alleged motive in his wife's shooting death.

Delisle, a former Quebec judge, is accused of first-degree murder in the 2009 shooting death of his wife Nicole Rainville.

His defence lawyer Jacques Larochelle on Wednesday focused on expert testimony presented by the Crown during the month-long trial. Nicole Rainville died in November 2009. (CBC)

Larochelle argued that ballistics experts who testified on weapon evidence omitted possible scenarios for how the alleged murder weapon was used.

Rainville was found dead in her Quebec City apartment in November 2009, with a gunshot wound in her head.

The defence also attacked the Crown's motive — that Delisle killed his ill wife because he was tired of caring for her, and wanted to start fresh with his long-time lover, his former secretary.

Rainville suffered a debilitating stroke in 2007, and then broke her hip in the months prior to her death.

The Crown also alleges that with Rainville's death, Delisle avoided a potentially expensive divorce from his wife.

Delisle's defence claims she was depressed in the aftermath of her stroke, and harboured dark thoughts.

Delisle initially reported her death as suicide. He was arrested several months later on murder charges.

His trial is the first time in Canadian judicial history that a member of the judiciary has been accused of first-degree murder.

The retired judge did not testify.

Delisle served as a judge for Quebec's Superior Court.

Crown prosecutors will present their closing arguments on Thursday.

The jury will receive instructions on Friday, before beginning their deliberations.