Nelson Hart was found guilty in 2007 of first-degree murder in the deaths of three-year-old twins Karen and Krista on Aug. 4, 2002, at Gander Lake in central Newfoundland.
Last month, a three-judge panel of the appeals division of provincial Supreme Court unanimously ruled Hart, now 44, should have been allowed to testify in a courtroom closed to the public during his jury trial.
The judges cited his "tendency towards epileptic seizures and his difficulty in thinking and speaking clearly under stress" and with many people around.
In a split 2-1 decision, the court ruled that a confession Hart gave during an elaborate undercover RCMP operation should not have been entered as evidence.
The provincial Crown applied Thursday to the Supreme Court of Canada for leave to appeal.
It will likely be weeks or months before the top court decides whether it will review the case. It does not explain why it grants or refuses leave in specific cases, but generally hears matters of national importance or those involving split judgments on important legal points.
The appeal judges were divided on the key question of whether a confession obtained as the result of a so-called Mr. Big sting was the result of improper coercion and inducements that violated Hart's rights under the Charter of Rights and Freedoms.
Two judges ruled the confession inadmissible. But one disagreed, saying "the tricks employed by the undercover police were not such as to shock the conscience of the community" and were not proven to be excessive coercion or inducement.
Hart at first told detectives that Krista fell in the water at a recreation area called Little Harbour. He said he didn't jump in to help because he could not swim.
Despite having a functioning cellphone in his car, Hart left his other daughter Karen behind as he drove about 11 kilometres to his home, passing a hospital and businesses, to get his wife who also couldn't swim.
Karen was dead and Krista was floating unconscious on the water by the time police arrived. She was later declared brain dead in a St. John's hospital where she was taken off a ventilator and died.
Hart changed his story two months later, telling police that he'd had an epileptic seizure and could not remember how his daughters wound up in the lake. He said he did not mention the episode earlier out of fear he would lose his driver's licence.
The investigation was stalled without other witnesses until the RCMP launched a sting known as Mr. Big in February 2005. Over four months and at a cost of about $413,000, officers posing as criminal gang members recruited Hart to travel with them across Canada. He met other fictitious mobsters, wined and dined at restaurants, casinos, racetracks and strip clubs, and sometimes moved what he thought was stolen property.
Hart has a Grade 5 education and was on social assistance before the sting began. He was taken to a Montreal hotel room on June 9, 2005, where an officer acting as gang leader asked questions about Hart's daughters as a feigned test of his loyalty.
In a 90-minute conversation that was videotaped and shown at his trial, Hart starts to describe his seizure but is cut off and told not to lie.
Hart goes on to say in detail how he planned to drown his daughters.
"I struck them with the shoulder, like that," he says on the recording that was made without his knowledge. He said social workers were planning to take his children and that, while he felt badly, he could not accept that his brother might get custody.
Hart is shown on another tape taking an undercover officer to the spot on the Gander Lake wharf where he re-enacts how he shoved the girls into the water.
Hart's defence lawyer argued in court that his client needed money, that he was paid more than $15,000 during the sting and that he was intimidated by the fake gang leaders.
St. John's lawyer Rosellen Sullivan helped craft the arguments that led to the appeal court order for a new trial.
Depending on what the top court decides, she said the Crown's options would be limited without the Mr. Big evidence that was crucial to their case against Hart.
"I would think there would be no chance for a new trial," Sullivan said in a recent interview. "That's in the abstract, of course, because what the Supreme Court of Canada does with it is a whole other matter."