A private detective has been hired to investigate an alleged murder of a Jewish underground fighter in 1947 by a British major.

He was a founder member of the SAS, was one of the most decorated officers of the Second World War, and has been hailed as a "legend among fighting men".

The heroism on the battlefield of Major Roy Farran, who died in 2006, earned him a Distinguished Service Order, three Military Crosses, the Croix de Guerre and the American Legion of Merit.

Now, however, his reputation is posthumously at risk again from a fresh investigation into the ugly incident, and friends fear that it may be tarnished for ever by the claim that Major Farran was the killer.

Steve Rambam, a private investigator from New York, has been hired by an unnamed Israeli living in America to reopen the case. He hopes to find Rubowitz's body, so that he can be given a proper burial, and discover more about who was responsible for the boy's murder.

He will soon visit Britain, where he hopes that five surviving members of the Palestine Police whom he has identified as members of the covert units might be willing to "clear their consciences" and reveal the burial place of their alleged victim. "There are people in the UK who have personal knowledge of the operations of these so-called 'snatch squads' because they were participants," Mr Rambam told The Sunday Telegraph.

Suspicions of Major Farran's involvement were first raised after his grey trilby hat, with his name written inside, was found near the Jerusalem street corner where witnesses said that Rubowitz was bundled into a car by a man carrying a pistol.

Major Farran commanded one of the police squads, while Rubowitz distributed fliers and posters for Lehi - the Jewish organisation nicknamed "The Stern Gang", which killed and wounded dozens of British officers as part of the campaign to drive Britain from Palestine.

Documents released recently by the Public Records Office appear to implicate Major Farran. A written statement from a more senior officer claims that Major Farran had confessed to having killed the boy during an interrogation, by "bashing his head in with a stone". However, Major Farran was tried for murder in 1947 and was acquitted for lack of evidence, a fact which has led some to accuse the British authorities of a cover-up.

Afterwards, he emigrated to Canada, where he maintained his innocence until his death. His family declined to comment to The Sunday Telegraph but Gerald Green, 80, a close friend who served alongside him in the Palestine Police, said he was innocent and the documents were a deliberate effort, perhaps concocted by a superior officer, to frame him.

In October 1947, the entire investigation file was burned by the British authorities in Palestine. Mr Rambam believes this was an officially sanctioned cover-up. But copies of some documents had been already sent to London, where they were kept secret for almost 60 years until being disclosed in 2005.