Prosecutors had powerful evidence to prove Robert Pickton was a methodical serial murderer who killed 26 women but a judge's ruling at his trial cut the case off at the knees, the Crown argued Monday in the B.C. Court of Appeal.

Prosecutor Gregory Fitch wants the Appeal Court to overturn a ruling by B.C. Supreme Court Justice James Williams, the trial judge, that allowed only six counts against Pickton to proceed, instead of the 26 Pickton is charged with.

That decision, said Fitch, hampered the Crown's ability to use similar-fact evidence to show the Port Coquitlam, B.C., pig farmer had a continuing scheme to kill drug-addicted prostitutes from Vancouver's Downtown Eastside.

Pickton's methods were planned and deliberate, said Fitch, essential elements needed to prove first-degree murder.

But Williams agreed to a defence application to sever 20 of the murder counts, ordering that they be tried later.

Fitch said that diminished the evidence available to the jury aimed at showing similarities among the type of victims, method of killing and disposal of the bodies.

The ruling left gaps in the Crown's case and allowed Pickton's lawyers to undermine the evidence in ways they otherwise would not have been able to do under the original undivided indictment, Fitch told the three-judge Appeal Court panel.

"It left the jury with a highly distorted picture of Mr. Pickton's conduct," he said.

"An efficient trial was achieved but in our submission it was achieved at the expense of a just one."

A jury convicted Pickton of the lesser charge of second-degree murder on all six counts at the end of a lengthy trial in December 2007.

Williams sentenced Pickton to life in prison with no parole eligibility for 25 years, the maximum allowable for second-degree murder but a sentence imposed automatically in first-degree convictions.

Pickton is appealing his convictions.

His lawyers argue, among other things, that he should get a new trial because Williams erred in his instructions to the jury and compounded those mistakes when jurors came back with a question suggesting they thought others might be involved.

The Crown filed a cross appeal, saying if the defence succeeds in getting the verdicts set aside and a new trial ordered, the Crown wants the new trial to hear evidence on all 26 first-degree murder charges.

Fitch said if Pickton loses his appeal and the Crown wins its application, it would ask that the order for a new trial be stayed since Pickton is already serving the maximum prison term.

Some of the evidence in the Crown's appeal includes material still subject to publication bans imposed before and during Pickton's trial.

But Fitch said the Crown's case on the 26 charges added up to a compelling body of evidence that would have demonstrated to a jury Pickton was guilty of first-degree murder on all of them.

"All of the victims fit a common and distinct profile," he said.

Pickton was arrested in February 2002. Police recovered thousands of bits of evidence -- from blood samples to bone fragments and victims' belongings -- from his ramshackle acreage in the Vancouver suburb of Port Coquitlam.

His method of operation was "singular in its brutality and utterly unique," said Fitch.

The women were shot, then butchered, their remains disposed of on the property or delivered to a rendering plant. It runs like a thread through all 26 counts and amounts to a signature or calling card, he said.

The defence has argued the Crown is only now bringing up the similar-fact issue because it wants to take a different tack in any new trial. But Fitch and his colleagues argued the prosecution raised it several times during Pickton's trial.

"The Crown had an overwhelming case these murders were planned and deliberate," said Fitch. "The jury never heard that case."

Both sides are expected to wrap up their submissions by the end of this week, though rulings on the complex duelling appeals are not expected soon.