MONTREAL - The trial of a Quebec judge accused of killing his wife continued on Wednesday as the prosecution's star witness picked apart the judge's defence: that his wife has committed suicide.

A ballistic expert who was examined over 7,000 firearms in his career, Gilbert Gravel was adamant that Nicole Rainville could not have killed herself with a tiny 22-calibre pistol.

The 71-year-old wife of magistrate Jacques Delisle was found dead in her apartment on November 12, 2009 with a gun next to her body. Enduring hardships after an accident, the woman had lost the ability to speak foreign languages and had wept much of the time she was in a Quebec City hospital.

In spite of her sadness, the woman never discussed the possibility of suicide according to a witness who described her hospital stay.

The case, which began on May 11, has revolved around a black gunpowder spot on Rainville's hand. Gravel said that Rainville would have had to have her hand on the barrel to be marred by the spot.

"I therefore exclude any possibility that her left hand was used to shoot in the left side of her head," said Gravel. The woman was paralysed on her right side by a stroke.

Gravel explained to the jury that someone else would have had to pull the trigger.

In another curious revelation on Wednesday, forensic biologist Jacynthe Prevost noted that if the gun was fired so close to the head, it should have been covered with blood. That wasn't the case.

Her theory: "If there was no blood, maybe the gun was cleaned."

The biologist was also puzzled by the blood pattern on the sofa, calling it inconsistent with a suicide.

The expert said that Rainville was likely turning her body and torso while receiving the bullet in her head, an indication she might have tried to protect herself from someone about to shoot her.

But under cross-examination, Delisle's lawyer Jacques Larochelle said that the biologist never went to the crime scene and strictly worked with photos. A scenario which he contended opened the door to errors.