OTTAWA — The Supreme Court of Canada will allow serial killer Robert Pickton to broaden his grounds for appeal on six murder convictions.

The high court formally said Thursday it will hear the appeal and will allow arguments on issues that go beyond the grounds which were the subject of a dissent at the appeal court level.

"Today's ruling is to give me the right to expand the grounds of appeal that I am going to be arguing in the spring," said Pickton's lawyer, Gil McKinnon.

"It's an expansion of the scope of the appeal and it permits the Supreme Court of Canada to deal with all of the issues that divided the B.C. Court of Appeal and not just the issues that the dissenting judgment was based on."

If Pickton's appeal is successful, he could win a new trial.

As usual, the court made no comment on its ruling.

Pickton was sentenced to life in prison with no parole for at least 25 years after a sensational trial in 2007 convicted him on six counts of second-degree murder.

The one-time pig farmer was convicted in the murders of six prostitutes but was charged in 20 other deaths, as well. Those charges were severed from the original trial and have never gone to court.

His lawyer argued at the British Columbia Court of Appeal that the trial judge's instructions left the jury confused on the question of whether Pickton acted alone.

The appeal court rejected the case in a 2-1 decision, but the dissenting judge said the jury instructions constituted a miscarriage of justice and would have ordered a new trial.

The dissenting vote gave Pickton a right of appeal to the Supreme Court, which was formalized in Thursday's announcement.

McKinnon now can expand his arguments beyond the question of the jury instructions.

"I wanted to expand the grounds by arguing some of the points raised in the majority's judgment which dismissed the appeal," he said.

"And there are three grounds specifically; one that the trial judge erred in not clarifying the jury's question before he responded to it, secondly that the main charge to the jury didn't contain any instruction on co-principal liability and third there were errors made with respect to similar-fact evidence.

"So those are the three additional grounds I will be able to argue in the spring appeal."

McKinnon said he doesn't think the expansion of the appeal grounds will delay the case, which is tentatively scheduled for March 25.