A former soldier jailed for life 16 years ago for the sex killing of a teenage boy was freed yesterday after his confession was shown to be unreliable.

The only evidence against George Long at his trial in July 1979 was the admission, quickly retracted, that he killed Gary Wilson, 14.

Psychiatrists told the Court of Appeal that Long had been suffering from a mental disorder which may have rendered the statement unreliable.

In part, they based their judgment on Army medical records, available before his trial but not put before the jury, showing him to be suicidal and prone to fantasy to boost his self-esteem.

The principal psychiatrist to give evidence on his behalf was Dr James McKeith, an expert on cases where defendants have made confessions and then retracted them.

The conviction was quashed by the Lord Chief Justice, Lord Taylor, sitting with two other judges.

Lord Taylor said: "The jury may well have thought the fact of the confession overwhelmed and transcended any other considerations. We simply do not know what impact the medical evidence might have had on the jury.

"It is sufficient to say that we were impressed by that evidence, supported as it was by records of mental disorder well before the murder."

Long was convicted, at the age of 20, of the murder of the schoolboy in Deptford, south-east London, in November 1978. The boy was beaten, stabbed and then mutilated after death, possibly with glass, sexually assaulted, partially stripped and dumped behind a derelict shop.

The case against Long rested entirely on confessions he made to police, without a solicitor's advice. He retracted the statements while in the police station, after consulting a solicitor, and continued to deny them at his Old Bailey trial.

He explained: "I thought if I admitted it you would go easy on me because you were scaring me."

Asked how he had been able to give details of what he said occurred, he replied: "You told me." When charged he said: "I didn't murder him. I just wanted to be put away."

Long's defence that the confession was "pure fantasy" relied on his own evidence.

Dr McKeith, who was instructed in 1992, examined Long's Army medical records which found him to be a "thoroughly depressing man" who was "afraid to use his personal weapon because he might shoot himself". Long was discharged.

There were also accounts of Long telling "fantastic tales about his exploits" to boost his self-esteem and impress others.

After his conviction, a prison medical officer found that he lived "in a world where fact and fiction are inextricably mixed". Dr McKeith told the appeal judges that Long had suffered from a mental disorder which rendered him "vulnerable and incapable of giving a reliable account".

Another psychiatrist for Long and one for the Crown essentially shared this view.

Michael Worsley, QC, for the Crown, accepted that, had the medical evidence been available to the jury, "it may well have had a significant impact".

The Crown sought to uphold the conviction on the basis that the confession contained details which only the killer could have known.

But Lord Taylor said he and his colleagues were not convinced that these details, all of which were disputed, "could safely be relied upon to demonstrate knowledge in the appellant only available to the murderer".

Members of Gary Wilson's family, including his mother, were understood to be in court but left without commenting.

Long said his belief in his innocence and hope that he would one day be freed had kept him going.

He added: "I have always thought of the boy's family. They have lost a son. That is a terrible loss. I can imagine the police going to the family home and saying: 'We have got the man who did it.' All their grief has been focussed into hatred towards me. I could feel their hatred in the courtroom. But I never killed that mother's son."