Hours after filing notice to appeal with the Alberta Court of Appeal, lawyers for Travis Vader sent a letter on Friday to Justice Denny Thomas, asking Thomas to declare a mistrial.

"What you're asking the judge to do is to set aside the decision and put people back to square one," Vader's defence lawyer Brian Beresh said Friday in an interview with CBC News.

That would mean setting aside Vader's convictions on two counts of second-degree murder in the July, 2010 deaths of Lyle and Marie McCann.  

"A mistrial can be granted in a number of circumstances," Beresh said. "But it occurs where somebody feels an injustice has occurred that is of such a serious nature that the trial cannot continue."  

Legal experts have weighed in across the country on social media to point out what they describe as a "fatal error" in the judge's decision, delivered Thursday.

Defence lawyer Brian Beresh is asking the judge to declare a mistrial in the Travis Vader case. (Rick Bremness/CBC News )

Section 230 of the Criminal Code, which Thomas used to convict Vader, was declared unconstitutional in 1990.

"We think because this error in law occurred, that it's time there be a mistrial," Beresh said.

Issue could be what charges to retry

Vader was originally tried on two counts of first-degree murder. Since Thursday's decision, legal scholars have been using social media to debate the issue of whether a new trial could be ordered on the same first-degree murder charges, since Thomas declared him not guilty on those counts.  

Beresh said he would take the position that Vader could not be tried again on first-degree murder charges.  

"Clearly, what would be triggered is our client's right to a trial in a reasonable period of time under Section 11b of the [Charter of Rights and Freedoms]," Beresh said.

"And as you know, the previous decision was we were getting very close to the time where a reasonable trial, or time for a reasonable trial, did not exist. So the extension time would be an issue another judge would have to consider."

Beresh said he thinks the earliest a new trial could be held would be in 2018.  

He said he has received no response to his request for a mistrial.  An Alberta Justice spokesperson also declined comment. 

'Chats' with Vader since convictions

Beresh says he's had "chats" with Vader since the the convictions Thursday.

"He's very disturbed about these events. Like everyone else he wants a decision, but a decision that's made fairly within the rules. We say that did not occur here."

Beresh said his client has new cause for optimism, given the possibility he may ultimately face a lighter sentence.

"I want to see whatever's done to be done fairly. Transparently. So that at the end of the day, everyone can say we trust this system of justice."

Removing provisions from Criminal Code

Successive federal governments have been sharply criticized for not amending the Criminal Code to remove unconstitutional sections.

In a 2010 British Columbia Court of Appeal decision, the judge wondered why those steps had not already been taken.

"It creates the risk of a miscarriage of justice and the potential need to incur significant costs addressing an error in an appellate court with the possible costs of a new trial," Justice Edward Chiasson wrote at the time.

"In my view, failure to deal appropriately with such matters … is not in the interests of justice."

Justice Minister Jody Wilson-Raybould says her department is looking at outdated provisions of the Criminal Code in a review that began earlier this year.

In a written statement provided Friday, federal Justice Minister Jody Wilson-Raybould said she asked department officials earlier this year to conduct a review of Criminal Code provisions for provisions that had been found unconstitutional "with a view to updating the Criminal Code to reflect these decisions."

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  Vader files notice of appeal on murder convictions

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  Vader convicted of 2nd-degree murder in McCann deaths