Sky News authorised a journalist to hack into the emails of '‘back-from-the-dead canoeist'’ John Darwin after ruling the action was in the public interest.
The broadcaster said the evidence it discovered was handed to police and used in the successful prosecution of Darwin's wife Anne for insurance and pension fraud.
Darwin, 61, faked his own death in a canoeing accident in 2002 so his wife, 60, could claim hundreds of thousands of pounds from insurance policies and pension schemes.
Former Sky News managing editor Simon Cole agreed that North of England correspondent Gerard Tubb could hack into Darwin's Yahoo! email account.
Mr Tubb uncovered messages that cast doubt on Mrs Darwin's claim during her criminal trial that her "domineering" husband forced her to go through with the fraud plan.
The Darwins, from Seaton Carew, near Hartlepool, were jailed at Teesside Crown Court in 2008 for the swindle, which deceived the police, a coroner, financial institutions and even their sons, Mark and Anthony.
In a separate case, Mr Tubb was authorised to access the emails of a suspected paedophile and his wife, although this investigation did not result in any material being published or broadcast.
John Ryley, the head of Sky News, said in a statement: "Sky News is committed to the highest editorial standards.
"Like other news organisations, we are acutely aware of the tensions that can arise between the law and responsible investigative journalism.
"On two occasions, we have authorised a journalist to access the email of individuals suspected of criminal activity.
"In the 2008 case of Anne Darwin, Sky News met with Cleveland Police and provided them with emails offering new information relevant to Mrs Darwin's defence.
"Material provided by Sky News was used in the successful prosecution and the police made clear after the trial that this information was pivotal to the case.
"We stand by these actions as editorially justified and in the public interest. We do not take such decisions lightly or frequently.
"They require finely balanced judgment based on individual circumstances and must always be subjected to the proper editorial controls."
Cleveland Police said in a statement: "Cleveland Police has conducted an initial review into these matters and can confirm that inquiries are ongoing into how the emails were obtained."
Sky News is part of BSkyB, which is 39% owned by Rupert Murdoch's News Corporation.
The Leveson Inquiry into press standards has heard that former Times reporter Patrick Foster hacked into the emails of Lancashire detective Richard Horton in 2009 to unmask him as the author of the anonymous NightJack blog.
James Harding, editor of the Times, which is owned by Mr Murdoch, told the inquiry in February that he "sorely regretted" the intrusion and "expected better" of his paper.
Mr Ryley said: "As part of our ongoing commitment to acting responsibly and in light of the current, heightened interest in editorial practices, Sky commissioned both an external review of email records at Sky News and an internal audit of payment records.
"While the email review is nearing its conclusion, no grounds for concern have been found. If evidence of impropriety was found, we would investigate immediately.
"We believe these pro-active steps, undertaken at our own initiative, form part of the good governance procedures to be expected of a responsible news organisation.
"At all times, Sky News remains focused on maintaining its high standards and delivering an outstanding service."