The body of Phoenix Sinclair, seen here in an undated photo, was discovered in 2006 on the Fisher River reserve.

A Manitoba couple found guilty in 2008 of killing five-year-old Phoenix Sinclair has lost a bid for an appeal.

The judgment was released Thursday by the Manitoba Court of Appeal.

"I would dismiss all grounds of appeal advanced by each accused and confirm their convictions for first-degree murder in the death of the child Phoenix Sinclair," stated the judgment, written by Justice Michel A. Monnin and co-signed by Justice Martin H. Freedman and Justice Richard J. Chartier.

Sinclair's mother, Samantha Kematch, and stepfather, Karl McKay, were convicted and sentenced in December 2008 in a case that made international headlines.

They are not eligible for parole for 25 years.

Submissions to the appeal court were made in October 2009.

In separate briefs filed with the court, Kematch and McKay argued they were unfairly convicted and should have been tried separately instead of together.

During the trial, defence lawyers did not deny the abuse Sinclair suffered at the hands of her parents but argued there was not enough evidence to convict the couple of first-degree murder.

The defence teams suggested that manslaughter was a more appropriate sentence because it was not clear who had delivered the final fatal blow to the little girl.

Body wrapped in plastic and buried

Sinclair was killed in the basement of a home on the Fisher River First Nation, about 180 kilometres north of Winnipeg. Her body was wrapped in plastic and buried in a shallow, unmarked grave near the garbage dump of the reserve.

During the trial, court heard that Kematch and McKay routinely beat Sinclair with their fists, feet and metal bars and forced her to eat her own vomit.

Sinclair was also choked until she passed out and was shot with a pellet gun.

Court was also told she had broken bones throughout her body when she died.

Her body wasn't found until March 2006, after police laid charges against Kematch and McKay and the latter showed RCMP the burial site.

Under the Criminal Code, a slaying committed while forcibly holding someone elevates the crime to first-degree murder rather than second-degree murder or manslaughter.

During submissions to the appeal court, lawyers for Kematch and McKay argued the girl was not physically locked in the basement and would frequently come upstairs to eat or play with siblings.

One of the defence lawyers suggested Sinclair may have stayed in the basement voluntarily to get away from her parents.

There were no locks on the doors, and no doors to the basement where she was kept, defence lawyers noted, adding that a complete lack of physical restraint means the conviction should have been reduced to second-degree murder or manslaughter.

That theory received a rough reception from the three appeal judges, one of whom said he had a hard time believing a young girl would want to stay in a basement away from her parents and siblings.