Key 'witness' was not called to give evidence: Although not in court during the trial of two policemen, the spotlight fell on Winston Silcott. Will Bennett reports

THE KEY figure in the month-long trial of Detective Chief Superintendent Graham Melvin and Detective Inspector Maxwell Dingle was not in court. Winston Silcott was not called to give evidence.

Despite warnings to the jury from the prosecution and the defence that they must not speculate on whether Silcott had murdered Constable Keith Blakelock during the Broadwater Farm riot, it was sometimes difficult to tell whether it was he or the defendants on trial.

The defence produced 14 hitherto undisclosed witness statements claiming that Silcott played a leading role in PC Blakelock's murder. One said: 'Silcott was carrying a knife with a blade about two feet long. He was cutting the police officer.'

Det Ch Supt Melvin and Det Insp Dingle did not give evidence. Apart from them only Silcott was present at the interview at Paddington Green police station, west London, on 12 October 1985, which led to the case. Only he could challenge their version of what was said.

Yet on the first day of the trial David Calvert-Smith, for the prosecution, told the jury that Silcott, cleared on appeal of the killing of PC Blakelock but still in prison for another murder, would not be giving evidence.

He said evidence from the scientists who had used the ESDA (Electrostatic Deposition/Detection Analysis) technique to allege that the detectives had altered the notes of the interview was sufficient.

Richard Ferguson QC, for Det Insp Dingle, accused the prosecution of not calling Silcott for 'tactical reasons'. He claimed that Silcott would either refuse to answer questions or that he would prove an 'unsatisfactory and unreliable witness'.

Increasingly there was an air of unreality about the proceedings. The case hinged entirely on highly technical evidence about ESDA, a technique which so far has proved more effective at getting convictions overturned than it has at securing them.

The technique, which enables experts to find out whether notes have been altered, has been crucial in several important miscarriage of justice cases such as the Birmingham Six and the three Ulster Defence Regiment soldiers jailed for a sectarian murder in Ulster.

It was developed in 1979 by Doug Foster and Bob Freeman, two research assistants at the London College of Printing, who came across it while trying to develop a new form of printing. But, despite having become well established over the last 15 years, ESDA has failed to convince juries to convict detectives in a series of police corruption trials.

Tom Davis, a lecturer and handwriting specialist at the University of Birmingham, said: 'The problem is not with ESDA itself, which is solid and as accurate as a photocopier, but with what is deduced from the fact that the indentation is there.'

Det Ch Supt Melvin, the most senior police officer to have faced a trial such as this, was always bullish about his prospects of acquittal. A detective of the old school, he treated the case with the determined, combative approach he brought to his own investigations.

He joined the police in 1960 and built up a formidable reputation with a string of commendations. He headed the inquiry which resulted in the serial killer Kenneth Erskine, known as the Stockwell Strangler, being sent to prison.

He was a natural choice to take over the Blakelock case, the largest murder inquiry in the history of the Metropolitan Police and one of the most sensitive, both because of the brutality of the killing and because junior officers believed that they had been poorly led during the riot.

Det Insp Dingle, who took the notes during the crucial interview with Silcott, spent 32 years in the police before retiring.

But as doubts grew about the convictions for the Blakelock murder they were investigated and Det Ch Supt Melvin was suspended in September 1991 when the convictions were referred back to the Court of Appeal. In 1992 criminal charges were brought against both men.