A woman already convicted with being an accessory after the fact in the death of Clifford Fair testified against the man charged with his murder on Thursday.

John Douglas Robinson has pleaded not guilty on the charge of first degree murder, but guilty to causing indignity to a dead body in the case.

Amy Gilbert, formerly known as Amy Gilbert-Cassidy, is considered a key witness for the prosecution.

She was convicted of being an accessory after the fact, but the Crown says she played no part in the murder.

Prosecutor Tom Meehan says her testimony is crucial, "Very much so, the eyewitness to the incident."

Gilbert testified that she and Robinson shared a basement apartment in a Princess Street home in the fall of 2008. Fair's remains were found buried in the backyard of that Woodstock home.

Gilbert told the court she invited Fair in for a few beers and everything was going fine when suddenly Robinson clubbed Fair on the head twice with a metal pipe wrapped at one end with cloth and duct tape.

She also said she had been in a relationship with the accused for about a year and a half and during that time Robinson was abusive, trying to strangle her twice and pushing her around a lot.

The Crown expects to call about 30 witnesses in the case, Meehan says, "There'll be witnesses that support her testimony and to incidents, conduct on the part of the accused after."

Gilbert cried repeatedly during her testimony, especially when shown a photo of the backyard where Fair was buried.

She told the court Fair was a good friend, that Robinson seemed jealous and that he smiled at her before swinging the pipe.

She also admitted that Robinson cried after the alleged incident, saying he never meant to kill Fair.

Trial began with graphic allegations

The trial in the murder began Wednesday with the Crown using opening statements to describe the grisly details in the case.

The dismembered body of Fair was found by forensic investigators in the backyard of the Princess Street home in the fall of 2008.

The Crown alleges Robinson hit Fair twice on the back of the head with the metal pipe, and that he and Gilbert then dragged the body there.

It is also alleged Robinson buried the body, but when he noticed part of it was exposed he exhumed, dismembered and reburied it.

The Crown contends Robinson wrote letters, and that he became panicked, believing Gilbert had told others about the crime.

The trial is expected to last about six weeks.