By Jon Silverman
Legal affairs analyst
Billy Dunlop was acquitted of the murder of Julie Hogg
In the briefest of retrials, Billy Dunlop has pleaded guilty to the murder in 1989 of 22-year-old Teesside woman Julie Hogg, having previously been acquitted of the crime.
The case is the first made possible by new legislation which allows what is known as "double jeopardy" in certain circumstances.
The double jeopardy rule, known in law as autrefois acquit, developed over centuries as a protection against oppressive prosecution.
Until the Criminal Procedure and Investigations Act 1996, there was an absolute bar on a case being reopened after acquittal.
That act introduced certain limited circumstances for a prosecution appeal, for example where the intimidation of either witnesses or jury had affected the outcome of a trial.
But no retrials have been sought under that provision.
'New and compelling'
It was the Macpherson inquiry into the murder of Stephen Lawrence which subjected the double jeopardy rule to scrutiny and recommended that prosecution after an acquittal should be allowed where "fresh and viable" evidence was presented.
In the 2003 act, this term has been changed to "new and compelling" evidence. What does it mean in law?
"New" signifies evidence which could not have been adduced at the original trial. "Compelling" means reliable, substantial and appearing to be highly probative of the case against the acquitted person.
To make the threshold high enough to deter attempts to reopen a case merely because there is a feeling, either amongst the police, or prosecutors, that a defendant "got off" unjustly, the question of whether there is fresh and compelling evidence has to be considered by the Court of Appeal on application from the Director of Public Prosecutions.
Interests of justice
The Dunlop case is the only one so far to have gone through that rigorous procedure.
However, other cases have been mentioned from time to time and after the relevant section of the Criminal Justice Act 2003 became law in April 2005, the National Crime Faculty speculated that up to 35 acquittals could be reviewed.
In deciding whether to overturn an acquittal, the appeal judges have to consider how the interests of justice are best served.
A priority is whether the defendant can get a fair trial the second time around, given the publicity and the length of time which has elapsed since the first trial.
The Appeal Court can prohibit reporting of the evidence put before it, although a jury will inevitably be told that they are trying a case which has already been heard at least once.
One safeguard for a defendant is that there can be only one application to have an acquittal overturned.
When the Law Commission recommended in 2001 that the double jeopardy law should be relaxed, it said that the only offence to qualify should be murder.
But the legislation applies to up to 30 offences which attract a life sentence, including manslaughter, kidnapping, rape, armed robbery and a number of serious drugs crimes.
Despite the government's agenda for "re-balancing" criminal justice in favour of victims, most lawyers and judges believe retrials after acquittal will be a rare occurrence.