The Supreme Court of Canada will rule Friday on whether or not serial killer Robert Pickton deserves a new trial.

Pickton was convicted in the murders of six women in British Columbia and still faces charges in the deaths of 20 others.

He was convicted in 2007 after an 11-month trial, but appealed his second-degree murder convictions on the grounds that the judge made a mistake in his instructions to the jury.

Pickton's lawyer, Gil McKinnon, argued at a hearing before Canada's highest court in March that the former pig farmer did not receive a fair trial when he was convicted in the deaths of sex-trade workers from Vancouver's squalid Downtown Eastside.

But B.C. prosecutor John Gordon told the high court that no errors were made by the judge at Pickton's trial -- and even if there were errors, they were so minor they do not warrant a new trial.

The Crown contends its case against Pickton was so overwhelming that he couldn't possibly avoid conviction at another trial, so justice would not be served by ordering a new one.

Central to the appeal is whether the initial instruction by the trial judge was adequate, and whether his subsequent answer to a question from the jury during deliberations further muddied the waters.

The prosecution has said that if Pickton's conviction is upheld, they will not proceed to trial on the remaining charges. If it is overturned, they want to retry Pickton on all 26 murder counts.

For families of the missing women, feelings are mixed about Friday's decision.

Roger Borhaven's daughter, Andrea Borhaven, is on the list of 20 women Pickton stands accused of killing but whose cases have not gone to court. He would like to see Pickton go to trial for his daughter's death, but he's also worried about a second trial.

"I'd sooner see him convicted. If he goes for another trial then he might get off," he said. "It's a gamble all right."

Either way, there will never be a trial for Pickton in the death of Dawn Crey. Police have not laid charges against Pickton in the cases of six women, including Crey, whose DNA was found on his farm.

Her brother, Ernie Crey, said he hopes the court upholds the convictions, but says it won't change anything if he's tried for another 20 murders.

"It can't make him any guiltier than he is," he said Tuesday.

"I hope his convictions are upheld and he faces his future as it is and that's basically a small cell in some federal prison for the balance of his life."

Crey said it's time to get on with a promised inquiry into the police investigation of dozens of cases of women missing from the poverty-stricken Vancouver neighbourhood.

In December 2007, Pickton was found guilty of six counts of second-degree murder and sentenced to life in prison for killing Mona Wilson, Sereena Abotsway, Andrea Joesbury, Georgina Papin, Brenda Wolfe and Marnie Frey.

Pickton is serving a life sentence with no possibility of parole for 25 years.

His 2002 arrest led to a massive search of his property in Port Coquitlam, B.C., where investigators found body parts, blood samples, fragments of bone and the belongings of victims.

The Crown's evidence was among the most grisly ever aired in a Canadian courtroom.