By Terri Theodore, The Canadian Press

VANCOUVER, B.C. - The Supreme Court of Canada has opened the door to a wider appeal for serial killer Robert Pickton, expanding the chances of a new trial for the B.C. man convicted in the gruesome murders of six women.

The high court announced Thursday that it will hear the expanded appeal, allowing Pickton's lawyers more legal grounds to argue that his convictions should be overturned when the case is heard in March of next year.

Normally, they would have been limited to the grounds that were subject of a disssenting view at the lower appeal court level.

In a two-to-one decision last June, the B.C. Court of Appeal rejected Pickton's bid for a new trial. But the dissenting judge said because the trial judge didn't provide the jury with an instruction of aiding and abetting - and how it applied to the Pickton case - there was a miscarriage of justice.

The dissenting opinion, by Justice Ian Donald, gave Pickton an automatic right of appeal to the country's highest court on the grounds he found in dispute.

But Pickton's lawyers asked the Supreme Court of Canada to go beyond the dissenting reasons, and consider if the trial judge made mistakes in both instructing the jury and in not clarifying the meaning of a question the jury posed to the judge during deliberations.

"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."

In the original trial, the jury came back on the sixth day of deliberations and asked the judge about inferring that Pickton "acted indirectly" in killing one or more of the victims.

The Crown had insisted throughout the trial that Pickton acted alone and did so until the jury came back with the question.

"I think there is much in what Pickton's counsel submits about the unfairness of the Crown changing its position at the terminal stages of the trial," Donald said in the B.C. Appeal Court ruling.

Donald said he viewed the Crown's behaviour as "scrambling to recover ground" by putting forward the theory that Pickton may not have acted alone only when the jury had problems with the idea that Pickton was the sole killer.

Robin Baird, the acting spokesman for the B.C. Crown prosecutors office, said the Supreme Court decision does open up the door to more legal arguments when the case is heard.

"It gives the Pickton team more grounds of appeal to work with."

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

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

Pickton was arrested in February 2002 after dozens of women from the Downtown Eastside vanished over more than a decade.

He was sentenced to life in prison with no parole for at least 25 years in 2007, after a sensational trial and conviction on six counts of second-degree murder in the deaths of women who vanished from Vancouver's seedy Downtown Eastside.

Pickton still faces charges in the deaths of 20 more women but those charges were severed from the original trial in order to simplify the very complicated jury trial, and those charges have not yet gone to court.

After Pickton was convicted, then-attorney general Wally Oppal said the Crown wouldn't proceed with the remaining 20 murder charges against Pickton unless the verdict was overturned.

Just last month, Mounties forwarded their final report to Crown counsel in the cases of six more women whose DNA was identified on Pickton's farm. He has not been charged in those cases.

B.C. Attorney General Mike de Jong said the high court's decision to hear expanded reasons for appeal from Pickton's lawyer won't change the Crown's strategy when it comes time to argue the appeal.

"We felt, and continue to feel, the Court of Appeal reached the appropriate decision based on the evidence that was provided at the trial level and we'll continue to argue that."

Many family members and friends of those women have called for an inquiry into why police didn't take the disappearances seriously.

Government officials have said any kind of inquiry would have to wait until the trial process is over.

In the case of killer Paul Bernardo an inquiry conducted shortly after his conviction found the police investigation was hampered by mistakes and rivalries between police departments.

But de Jong refused to compare the two cases.

"At this stage we're still focusing our efforts and resources on the prosecution of the matter."