On behalf of his family, Bret McCann expressed gratitude and relief Monday that his parents' killer, Travis Vader, has been found guilty of manslaughter.

"I was really glad that it was not a mistrial," McCann said. "We're comfortable that justice is being served. I want people to know that our institutions do work. From the police to the Crown to the court system."

Two second degree murder convictions against Vader for the July 2010 killings of Lyle and Marie McCann were vacated Monday in an Edmonton courtroom. The judge who heard the case instead substituted guilty verdicts on two charges of manslaughter.

"At the outset, I had indicated that I accepted that Mr. Vader was incorrectly found guilty of second degree murder, based on Section 230 of the Criminal Code of Canada," Court of Queen's Bench Justice Denny Thomas said.

"Therefore, I vacate my findings that Mr. Vader is guilty of second degree murder and the related convictions. Mr. Vader, I substitute verdicts of guilty on the lesser and included offences of manslaughter."

Vader was convicted on Sept. 15 in the deaths of the McCanns. The elderly St. Albert couple disappeared more than six years ago on a road trip to British Columbia. Their bodies have never been found.

During the trial, Thomas said evidence proved that Vader robbed and shot the couple. But he did not find that the drug addict intended to kill the McCanns.

Bret McCann, son of the missing couple, said Monday he's relieved by the manslaughter verdict, but will be happy when the court case is over. ((CBC))

To convict Vader on the murder charges, the judge relied on Section 230 of the Criminal Code, which was struck down in 1990 as unconstitutional.

That led to a defence application for a mistrial.

Vader's lawyers characterized the judge's mistake as "a colossal error" and insisted it could only be fixed by dropping the guilty verdicts and ordering a new trial.

The judge admitted he made a mistake. Near the beginning of the hearing, Thomas referred to his use of the unconstitutional Criminal Code section.

"I certainly accept that is an error," Thomas said.

But after listening to legal arguments from the Crown and defence, it only took Thomas 20 minutes to return to the courtroom with his decision to vacate the second degree murder convictions and substitute findings of manslaughter.

Sentencing hearing next

Thomas has set aside at least one week beginning Dec. 12 to hear from the Crown and defence for a sentencing hearing. There is a wide range for manslaughter convictions, from a suspended sentence, to time already served, to life in prison.

Prosecutor Ashley Finlayson hinted he will ask for a harsh sentence.

Travis Vader was convicted of manslaughter on Monday in an Edmonton courtroom. (CBC) "I think it's fair to say there's two manslaughters that we're going to be asking for something at or near the upper end of the range," Finlayson said.

Vader's lawyer, Nate Whitling, said outside court it's possible the defence will ask for the convicted killer to be let out of jail immediately with time already served.

Whitling also expects to appeal Thomas's decision.

"It's our view Justice Thomas did not have the authority to do this," he said. "This is a matter that is going to have to be sorted out by a higher court down the road. Our own view is that there needs to be a new trial altogether. We may well be asking for an acquittal as well."

Bret McCann and the rest of his family will be able to deliver victim impact statements at the sentencing hearing.

"They need to recognize his total lack of remorse and the lies," McCann said. "Like where are the bodies of my parents? I want to see that he mans up to what he's done here.

"I totally want this to be over. I totally want to be able to move on."