William Dunlop had got away with murder – twice.
So why did he confess, and how did that lead to an 800-year-old law being changed?
In 1999, Dunlop made a dramatic disclosure to a prison guard.
He was one year into a seven-year stretch for grievously wounding his partner and her ex, when he admitted he was also a murderer.
Ten years earlier, Dunlop had gone to the home of 22-year-old Julie Hogg, in Billingham, County Durham, and strangled her, before sexually mutilating her body and hiding her beneath the bath.
The revelation that he was the killer came as little surprise.
In 1991, he had twice stood trial for the 1989 murder, but both times jurors had failed to reach verdicts – with the second trial resulting in a formal acquittal.
The double jeopardy rule, an established common law practice, states a person cannot be tried for the same crime twice after a previous acquittal.
So when Dunlop made his confession, he knew he could not be prosecuted for Julie’s murder.