Despite his known false confessions to a dozen other killings - including the murder of Hilda Murrell, the peace campaigner, and a death fabricated by a psychologist - a jury had convicted David McKenzie of manslaughter solely on his own admissions.
Yesterday Lord Taylor, the Lord Chief Justice, sitting with Mr Justice Simon Brown and Mr Justice Roch, ruled the confessions totally unreliable and said that they should not have been put before a jury. They had been told that, motivated by bizarre feelings of guilt, he was a 'serial confessor not a serial murderer'.
In the past, uncorroborated confessions had led to miscarriages of justice, Lord Taylor said. He ruled that, in future, courts must throw out a case when three conditions apply - when a prosecution depends wholly upon a confession; when a defendant suffers mental handicap; and when the confession is unconvincing. Until yesterday's ruling, judges have maintained a discretion to allow the case to proceed.
The ruling was welcomed by Paul Bacon, McKenzie's solicitor, as a recognition by the courts that certain types of vulnerable people 'need protection from themselves'. But lawyers are hoping that the Royal Commission now examining the criminal justice system in the wake of the series of miscarriages of justice will go further and outlaw all uncorroborated confessions.
McKenzie, 38, who was in court to hear his convictions quashed, remains at Rampton top-security mental hospital in Nottingamshire because the judges rejected his further appeals against conviction for two arson offences. However, Mr Bacon is hopeful that a mental health tribunal will recommend his release to a special hostel, now that the manslaughter convictions have been overturned.
McKenzie, of Pimlico, south-west London, had been convicted at the Old Bailey two years ago for the manslaughter through diminished responsibility of Barbara Pinder, 76, of Battersea, and Henrietta Osbourne, 86, of Chelsea.
Lord Taylor said that, although McKenzie had given great detail of the two killings, his alleged special knowledge could have been gleaned from the massive publicity and knowledge of the area. He had omitted to mention significant details, including that a pen and knitting needle had been left in the bodies. The jury had been given the impression that McKenzie would also be charged with killing Miss Murrell, and this may have influenced it.