Her car has broken down and she is all alone. Young, attractive and in distress, she looks fetchingly at a young man leaving work and asks if he would be so good as to help.

He obliges.

Before they part, she hands him her phone number, then smiles with the unspoken promise of future romance.

He cannot believe his good fortune. But in reality, the woman is an undercover RCMP officer, and soon he will be in a prison cell.

This is a real-life example of a controversial Canadian police technique known as the Mr. Big sting. It came from the trial of two men connected to the slaying of four RCMP officers in March 2005 near the Alberta hamlet of Mayerthorpe.

This week, the technique was in the news again after Canada's Justice Minister, Rob Nicholson, ordered a new trial for Kyle Unger, 38, of Manitoba, ruling he was probably a victim of a miscarriage of justice.

Unger has spent 14 years behind bars after being convicted of the sex murder of his former high school acquaintance, Brigitte Grenier, in 1992 at a bush party near Roseisle, a hamlet in south-central Manitoba.

In stings like the one used against Unger, undercover police officers connect with a target and then introduce him to Mr. Big, a man posing as a major mobster. The target is invited into Mr. Big's crime group, but only if he will admit committing a major crime.

The target in the Mayerthorpe case was drawn into an elaborately staged plot that involved a bogus beating, pretend gun running, cigarette smuggling and diamond stealing. One Mountie even played the role of Santa at a fake company Christmas party.

After Shawn Hennessey and Dennis Cheeseman were convicted of murder for helping the actual killer in the Mayerthorpe case, Barry Hennessey, father of Shawn and father-in-law of Cheeseman, revealed that Cheeseman had sometimes feared for his safety because he thought he was dealing with bona fide organized criminals.

"He was scared for his life,'' Hennessey told reporters. "He thought they were Hells Angels."'

Critics of the Mr. Big technique argue the police stings often lead to false confessions by people seeking to make illegal money.

Rubin (Hurricane) Carter of Toronto-based Innocence International calls Mr. Big stings a dangerous threat to civil rights, which can easily slide from evidence-gathering to entrapment.

"They've ... convicted people who were not guilty of crimes," says Carter, who served 20 years in prison in the U.S. for a murder he did not commit.

Carter says he doesn't doubt that such stings have bagged many real criminals as well, but he says the price for the tactic is too high.

Critics like Carter say modern-day Mr. Big operations aggressively entrap targets like Unger with threats and the lure of big money as a mobster. Carter notes such stings are illegal in both Britain and the U.S. because they actively induce someone to join a criminal enterprise they would not otherwise have joined.

In Unger's case, serious doubts about his conviction led to his release from prison late in 2005, pending a review.

Among other things, DNA tests proved a hair found on Grenier's clothing wasn't from Unger, even though an RCMP hair analyst told the jury it was "consistent" with Unger's hair.

Unger's lawyers also argued that police extracted a false confession from him during a Mr. Big operation.

In the scenario that was used to ensnare him, two undercover police officers staged a vehicle breakdown at the farm where Unger worked. While they waited for repairs, they pretended to recruit him into a criminal organization where they suggested he could make big money with little work.

Soon, he was acting as their chauffeur, picking up and dropping off mysterious packages. Unger, who already had a drinking problem, moved into a penthouse with a well-stocked liquor cabinet. Mr. Big was introduced to him as "Big Larry," who told Unger in a recorded conversation: "(Another undercover officer) tells me you whacked somebody. That's fine with me. That's, that's f---ing excellent ... That's the kind of person I'm looking for."

Unger didn't correct Big Larry. Soon, he was telling another undercover officer that he was Grenier's killer, offering vivid details and taking him to the crime scene. He showed them a bridge where he said he killed Grenier, apparently unaware the bridge didn't exist at the time of the murder.

Unger later said he lied to impress Big Larry and to gain more money as a member of his organization.

"The difficulty with these details is that they were not true," Justice Holly Beard of the Manitoba Court of Queen's Bench noted in her judgment.

Another Mr. Big sting ended in a murder conviction earlier this year against Penny Boudreau, 33, of Bridgewater, N.S., who had strangled her 12-year-old daughter, Karissa, with twine.

Boudreau was drawn into a Mr. Big sting after she and her boyfriend were jailed on suspicion of Karissa's murder. An RCMP officer posed as her boyfriend's cellmate, and gave the impression he had serious organized crime connections.

Once Boudreau and her boyfriend were released, she couldn't stop thinking about news reports that speculated that DNA testing would lead police to the killer.

The DNA was supposed to be on Karissa's clothing, which was in a police evidence room.

On May 8, 2008, she turned to an associate of her boyfriend's former cellmate. He carried himself like a major mafioso, who bragged he could get difficult things done.

Boudreau told him she wished the "police exhibit vault would burn down or blow up." The police officer playing Mr. Big said he needed to know more about the crime in order to make the evidence vanish.

Boudreau's admissions were the main reasons she was sentenced to life in prison with no chance of parole for 20 years.

A Mr. Big sting also closed the case on the murder of Ajax security guard Roy Jones, who was gunned down execution-style in Whitby in 2001, just days before he was due to testify in a home invasion trial.

Soon, men who looked like bikers and called themselves Jake and Mick had moved into a Brantford apartment building next door to one of the suspects, Sean Hall.

In reality, they were Durham police officers. To Hall, they looked like outlaw bikers and he soon introduced himself. They didn't push Hall to talk. Instead, they sometimes told him to shut up. "You talk too much," Mick told him in one recorded conversation.

Hall felt an urge to impress them, and told them he had been involved in a murder. "The cops have nothing," he bragged.

One of Hall's friends warned that his new biker friends might actually be police officers.

"If they are, they are wicked actors," Hall replied, shortly before his arrest.