A man whose manslaughter conviction has been quashed cannot be told why he was the victim of "a serious miscarriage of justice", judges have ruled.
Shaun Booker, 36, of Dryden Road, Sheffield, was jailed in 2002 over the death of 57-year-old Michael Marples.
But new information meant the conviction could not stand, London's Criminal Appeal Court heard on Monday.
However, the reason could not be given without causing "serious damage to the public interest", judges said.
"We acknowledge this must be less than satisfactory for Mr Booker, but it is a course we are bound to take in the public interest," said Lord Justice Keene, sitting with Mr Justice Stanley Burnton and Sir Richard Curtis.
Before the judges gave their decision, Mr Booker's barrister, Richard Barradell, urged them to reveal as much as possible about the new evidence.
"I submit he is entitled to know in the fullest possible terms why it was he was subjected to what he was subjected to," Mr Barradell said.
Lord Justice Keene said there was no dispute that in the early hours of 19 June, 1999, someone assaulted Mr Marples in the car park of the Trades and Labour Club in Sheffield. Mr Marples suffered skull and brain injuries from which he died.
At trial, Mr Booker denied assaulting Mr Marples.
"He said he saw him on the ground, went to help, trying to put him in the recovery position," the judge said.
"On the evidence before them, the jury was clearly satisfied as to be sure that the assailant was Mr Booker.
"However, other evidence has emerged since the trial which casts very great doubt on the correctness of the appellant having been the assailant."
Lord Justice Keene said the Crown had claimed "public interest immunity" for the documentation, which resulted in the new evidence coming to light.
"We are satisfied...that the nature of the evidence is such it cannot be disclosed without causing serious damage to the public interest," he said.
"The Crown made it clear they would have abandoned the case against Mr Booker if the new evidence had been available.
"This conviction cannot stand, in light of the new material."
"It goes without saying, there has been a serious miscarriage of justice, one can only profoundly regret that it has happened."