A controversial police tactic behind several high-profile criminal convictions, including that of Daniel Morcombe's killer, is under a renewed legal threat that could have repercussions in Australia.
Police have long relied on elaborate ''Mr Big'' stings to nab killers who have dodged all other attempts to catch them. The technique uses undercover officers to pull suspects into a fake criminal gang, sometimes for years, until they eventually confess to murder.
But Canada's highest court has heard a legal challenge, arguing the technique can lead to false confessions and violates both a right to remain silent and a right against self-incrimination.
The court's decision, expected within days, could rewrite the rules on how such undercover police operations are conducted and have ramifications in Australia, according to several lawyers in both countries familiar with the case.
Brisbane criminal defence lawyer Tim Meehan said: ''Any change in the validity of the Mr Big scenario in Canada will have a flow-on effect in Australia.''
Melbourne lawyer Rob Stary agreed, saying Mr Big stings have been criticised for years. The police tactic created by Canadian police in the 1990s was adopted in Victoria to solve at least four unsolved murders.
In 2011, Queensland police also used the ploy to persuade Brett Peter Cowan to confess to murdering schoolboy Daniel Morcombe. He was convicted in March, but Mr Meehan has filed an appeal, citing many of the same concerns now before the Canadian courts.
Russell Silverstein, co-director of the Association in Defence of the Wrongly Convicted, said Australia and Canada had previously raised legal issues over Mr Big stings, but the current case is the largest legal test. ''This is going to have a big impact on how police conduct their business,'' he said, noting the US has already banned them.
The case involves Nelson Lloyd Hart, a lonely Newfoundland father with a limited education who confessed to killing his twin daughters after being showered with cash, fancy dinners and friends during a four-month police sting.
But Paul Holdenson, QC, who was involved in an unsuccessful Australian High Court challenge in 2007, questioned if anything could be done to stop the practice.