David McKenzie, 37, was a 'serial confessor rather than a serial killer', said Geoffrey Robertson, QC, his counsel.
Evidence showing that David McKenzie could not have killed 78-year-old Miss Murrell was only revealed to his lawyers last week. Yet the jury which convicted him two years ago of killing two other women - Henrietta Osbourne, 86, and Barbara Pinder, 76 - was led to believe that he would also face trial for the murder of Miss Murrell.
In fact it was known that the man who killed Miss Murrell and masturbated over her body had undergone a vasectomy. McKenzie had a high sperm count.
Controversy has surrounded the 1984 Murrell killing, after suggestions that the security services were involved.
Yesterday, the court heard that the Murrell confession came among a string of others by McKenzie, including admissions to the killings of Mrs Osbourne and Mrs Pinder, taken during a week of police questioning and in the absence of a solicitor.
Two confessions were shown to be false because McKenzie was found to have been in hospital at the time. He also 'confessed' to a murder fabricated by a psychologist to test McKenzie's suggestibility.
Mr Robertson said McKenzie was unable to distinguish between fact and fantasy. He had a disturbed childhood, and had deep feelings of guilt manifested in a desire to confess to crimes.
'We say that the doubt in this case not so much lurks as shrieks,' Mr Robertson told Lord Taylor, Mr Justice Simon Brown and Mr Justice Roch.
What was deeply worrying, said Mr Robertson, was that the confessions - the only evidence against him - were allowed to go before a jury in the first place.
The trial judge had a common law duty to withdraw charges based on uncorroborated confessions from a mentally disordered defendant, when there was significant risk of their unreliability, he argued.
There was nothing in his confessions that McKenzie could not have picked up from the press or from local comment on the cases.
Because of his mental disorder McKenzie, of Vincent Road, Pimlico, south-west London, had originally been found unfit to plead. But in 1990, he stood trial at the Old Bailey after doctors ruled he had recovered sufficiently to distinguish between fact and fantasy.
He was convicted of manslaughter, through diminished responsibility, and was ordered to be detained in Rampton hospital.
If his present appeal is allowed, he will remain in Rampton - a hospital order was also made against him for entirely separate sex offences.
The appeal continues today.Reuse content