07/31/2014 06:52 EDT | Updated 09/30/2014 05:59 EDT

FactBox: Some prominent cases featuring Mr. Big stings

The Supreme Court of Canada ruled Thursday that confessions extracted through so-called Mr. Big police sting operations tend to produce unreliable confessions and are open to abuses. The investigative technique involves undercover police officers who recruit a suspect to a fictitious criminal organization while posing as gangsters and the aim is to obtain a confession to a crime. The high court ruling was triggered by the case of Newfoundland's Nelson Hart, who had been convicted of drowning his twin daughters in a case involving a Mr. Big Sting. The conviction was overturned in appeal court. The Supreme Court on Thursday ruled that Hart's admissions during the sting cannot be used against him should he face another trial. One of his lawyers said he expects his client will go free.

Some other cases that featured Mr. Big stings include:

Penny Boudreau: When her 12-year-old daughter Karissa vanished from the Nova Scotia town of Bridgewater, Boudreau earned public support as a grieving mother. Police, however, suspected she knew more than she claimed. After Karissa's body was discovered, police set up a Mr. Big operation to investigate their suspicions. Penny Boudreau eventually not only confessed to the crime, but re-enacted it for undercover officers and provided a detailed written account of her daughter's final moments. She admitted to strangling Karissa over the child's cries of "Mommy, don't." Boudreau pleaded guilty to second-degree murder in 2009. She is now serving a life sentence.

Shawn Hennessey and Dennis Cheeseman: The two men who helped James Roszko, the man who killed four RCMP officers in Alberta, were ensnared in a Mr. Big sting years after the killings. The brothers-in-law drove Roszko to the site of the farm where he ultimately shot and killed the four officers before turning the gun on himself. The sting operation featured a female undercover officer posing as a femme fatale, who had her car break down in front of Cheeseman's workplace. She eventually lured him into a fake crime gang composed of undercover Mounties. Together, they "stole'' a boat, stole cigarettes, and shipped guns. Cheeseman pocketed hundreds of dollars. Eventually, the gang brought up the slayings. They told Cheeseman they had satellite photos of him dropping off Roszko. He confessed all and eventually drew Hennessey into the gang. With the promise of a big payday in another crime operation, Hennessey, too, revealed his role. The pair eventually pleaded guilty to manslaughter in 2009.

Atif Rafay and Sebastian Burns: The two British Columbia teens, who became friends while attending high school, were convicted of killing Rafay's parents and disabled sister at their home in Bellevue, Wash. The accused initially told police that they had found Rafay's relatives dead after an apparent break-in in July 1994. But confessions extracted during an RCMP Mr. Big operation ultimately led to their convictions in a Washington State court. Lawyers for Burns and Rafay argued details from such stings are not admissible in U.S. courts and the men, who were 18 at the time of the killings, were coerced into admitting to the murders. But a panel of three judges has ruled proper U.S. legal standards were applied in accepting the sting evidence and that a lower court was right to decide Burns and Rafay confessed voluntarily. The men are currently serving life sentences for the killings.

Nathan Fry: The Supreme Court of British Columbia heard details of how the 18-year-old deliberately set a house fire in 2006 that killed five people in east Vancouver, including a mother and her three children. Those details, however, were first relayed to police who persuaded Fry that he was a rising star in a criminal organization. In a videotape made by undercover police and shown in court, Fry said he bought fuel from a gas station, broke a window at the home, dumped the gasoline and used a torch to ignite the blaze. He was found guilty in 2008 of five counts of first-degree murder.

Kyle Unger: A confession extracted during a Mr. Big sting was among the pieces of evidence used to wrongfully convict Unger for the 1990 murder of Manitoba teen Brigitte Grenier. The details of the confession began to unravel years after Unger was found guilty. The account Unger shared with undercover officers contained several factual holes, including references to a bridge that had been built several months after Grenier's death. DNA tests later cast further doubt on Unger's guilt by proving the only physical evidence in the case could not have come from him. In 2009, the federal justice minister determined that the conviction had probably been a miscarriage of justice. Months later, Unger was formally acquitted.

Unsuccessful sting: The RCMP thought they had successfully solved the double-slaying of Barry Boenke and Susan Trudel, who were found beaten to death on their Edmonton-area property in 2009. They had set up a Mr. Big operation and extracted a confession from a teenage suspect. But four years later, prosecutors had to stay charges of second-degree murder after Judge Brian Burrows ruled the confession was inadmissible. He said officers had given the psychologically troubled teen money, beer, access to a condo, tickets to a hockey game and a rock concert and a snowboarding trip to the mountains. Burrows ruled the undercover officers had such a hold over the boy that he was effectively in custody. As a result, his confession violated his constitutional right against self-incrimination.