EDMONTON -- A judge has changed his flawed murder verdict to manslaughter in the high-profile case of Travis Vader -- a satisfying fix for the family of two missing seniors he was convicted of killing, but one the defence says is bound for a higher court.

Queen's Bench Justice Denny Thomas convicted Vader in September of second-degree murder in the deaths of Lyle and Marie McCann.

The couple, in their late 70s, disappeared after setting out from their Edmonton-area home to go camping in British Columbia in July 2010. Their burned-out motorhome and a vehicle they had been towing were discovered in the days that followed. Their bodies have never been found.

In finding Vader guilty of murder, Thomas mistakenly used Section 230 of the Criminal Code, which the Supreme Court declared unconstitutional in 1990. The government didn't remove the section from the book as antiquated laws are rarely repealed.

"I accept that it was an error," Thomas told court Monday as lawyers argued over whether there should be a mistrial.

He then quickly vacated the murder verdict and found Vader guilty of manslaughter instead. The judge gave no reasons and said a written decision would come later.

"I am glad to see this come to an end," said Bret McCann, the couple's son, when reached by phone.

He said a manslaughter verdict still means Vader will be going to prison and the public will be safe. It may also mean more answers.

"At some point in the future, he will be looking for parole, and I am hoping that he shows remorse and lets us all know where my parents' bodies are."

Thomas said in his original verdict that Vader was a desperate drug addict who came across the couple in their RV and shot them during a robbery. He said he found no evidence Vader intended to kill the McCanns and ruled out a planned and deliberate first-degree murder.

Section 230 allowed for a second-degree murder verdict if a killing occurred during the commission of another crime such as robbery. Otherwise, there had to be intent to cause death or bodily harm known to likely cause death.

Law experts have said a judge has never before cited the old section in a verdict and the mistake was huge.

The Crown argued the judge could fix the error by using another section of the Criminal Code to convict on second-degree murder or by substituting the verdict with manslaughter.

The defence said a mistrial was the only real remedy.

"We're quite disappointed with the decision," lawyer Nathan Whitling said outside the courthouse. "This is a matter which is going to have to be sorted out by a higher court down the road."

He expects to ask the Court of Appeal for a new trial or possibly an outright acquittal.

The case has been plagued with problems since the beginning, Whitling added.

There were some missteps by RCMP during the initial investigation. The Crown then stayed the murder charges just before a trial was to begin in 2014, because Mounties hadn't disclosed all evidence to lawyers. The charges were relaid nine months later.

Vader has filed lawsuits claiming malicious prosecution, as well as mistreatment by guards while in custody.

Whitling said that during the sentencing hearing, which is to begin Dec. 12, he is likely to ask the judge to consider the time Vader has already spent in custody and the abuse he has allegedly suffered.

Prosecutor Ashley Finlayson wouldn't reveal what sentence he plans to ask for, but that it would be near the top.

There is no minimum or maximum sentence for manslaughter. If sentenced to life for the crime, a killer can apply for parole after seven years, minus time spent in custody.

Judges make mistakes, Finlayson said, but there can still be justice.

"I think the public should be confident the system is working," he said.

-- With files from John Cotter