VANCOUVER, B.C. - The evidence against convicted serial-killer Robert Pickton was "overwhelming," and he does not deserve a new trial on six counts of murder, say B.C. prosecutors.

In their brief to the Supreme Court of Canada ahead of Pickton's appeal next week, the Crown lawyers said evidence against Pickton is so strong that a retrial would undoubtedly produce a guilty verdict.

"The weight of the evidence against Pickton is staggering," said the factum filed with the country's highest court, which is scheduled to hear the appeal next Thursday.

"He is a self-confessed killer. He admitted he was caught because he became sloppy at the end ....

"That Pickton is the person responsible for this scheme is inescapable ... The evidence leads to only one conclusion - the six victims shared more than a common profile; they shared a common fate at the hands of a common perpetrator ..."

Pickton was found guilty by a jury in 2007 of second-degree murder in the deaths of six women from Vancouver's poverty stricken Downtown Eastside, and sentenced to 25 years. He was originally charged with 26 counts of first-degree murder, but the trial judge severed the other 20 cases from his trial.

He is appealing to the high court to overturn the convictions and order a new trial, mainly on grounds the trial judge didn't properly instruct jurors.

That would be a mistake, said the B.C. Crown.

"Ordering a new trial in this case, where conviction is inevitable, would serve only to 'detract from society's perception of trial fairness and the proper administration of justice."'

Pickton's lawyers argue B.C. Supreme Court Justice James Williams gutted Pickton's defence when he amended his instructions after the jury came back with a question on Day 6 of their deliberations on whether they could convict him if he acted indirectly in the killings.

Williams' initial instructions, crafted after hearing defence and prosecution submissions, told the jury it had to find Pickton guilty if he was the "actual shooter."

After the jury's question, the judge amended his instructions to say that Pickton was guilty if the jury found he had "actively participated in the killings," which the defence claims opened the door to an aiding and abetting angle it hadn't prepared for.

The B.C. Court of Appeal upheld Pickton's conviction 2-1, but the dissenting judge agreed with the defence, saying the judge's error set up a miscarriage of justice.

In its submission to the high court, the Crown argues that if anything, Pickton benefited from whatever procedural errors or evidentiary rulings Williams made, which "blunted" the prosecution's case during the 11-month trial.

"Robert William Pickton was properly convicted of murder following a trial that was fair in substance and appearance," it said. "In fact, in many respects, the trial was unduly favourable to him."

Far from opening an unforeseen route to his conviction, the judge's amended instructions to the jury simply clarified an obvious fault in his original instructions that the jury rightly perceived, the Crown's submission says.

Crown lawyers said there was overwhelming evidence that Pickton, and only Pickton, was at the centre of an "inhuman" scheme to murder and dismember vulnerable women.

"In fact, much of it came out of Pickton's own mouth. He said he was the 'head honcho' and that others were 'involved too.' "

The B.C. Attorney General's Ministry has said if Pickton wins a new trial, the Crown would re-file the indictment to include the 20 counts Williams severed before the trial.