TORONTO - The first-degree murder conviction for a man who raped and killed an elderly woman in a motel in Guelph, Ont., 20 years ago will stand, the province's highest court ruled Friday.

Wayne Robson was sentenced to life in prison in 2005 for the killing of 77-year-old Pearl Pettitt in 1988. At his original trial, Robson admitted to killing and sexually assaulting Pettitt, but he maintained he didn't remember the incident because of an alcohol-induced blackout.

In the appeal, Robson, who was 19 at the time of the murder, alleged the trial judge erred in two different instructions to the jury, but the Ontario Court of Appeal disagreed.

The judges cited a number of reasons for why they disagreed, including the fact that experienced defence lawyers at the original trial didn't object to the instructions at the time.

Pettitt was found dead in her room at the Parkview Motel in December 1988, but Robson was not charged with the crimes until 2004. He had been ordered to provide a blood sample following convictions in 2003 for two bank robberies in Guelph.

His DNA was compared to samples collected from the motel crime scene in 1988, and he was charged with the killing in early 2004.

Robson, now 37, and a fellow inmate at Collins Bay Institution recently pleaded guilty to manslaughter in the death of another inmate in October 2003.

Robson, who admitted to stabbing Robert Bruce a number of times, was sentenced to 15 years, to run concurrently with his life sentence for killing Pettitt.