One of the sounds matches the echo pattern of a test shot fired from the grassy knoll

DB Thomas

A British forensic scientist backs the so-called "grassy knoll" theory that a second gunman shot at the president at exactly the same moment as assassin Lee Harvey Oswald fired three shots from a book depository.

The scientist, DB Thomas, has examined recordings of radio channels used by police in the Texas city of Dallas, where the murder took place.

In his article, he says five separate gunshot sounds can be heard on one of the tapes at exactly the time the president was killed.

'Mistakes'

Mr Thomas says mistakes were made in synchronising conversations on the two police frequencies, leading earlier investigations to dismiss the theory that a second gunman opened fire from a grassy knoll overlooking the presidential motorcade.

This is an honest, careful scientific examination of everything we did, with all the appropriate statistical checks

G Robert Blakey

His article is published in Science and Justice, the journal of Britain's Forensic Science Society.

"One of the sounds matches the echo pattern of a test shot fired from the grassy knoll," he writes in his paper.

That was also the key finding of a congressional investigation by the House Committee on Assassinations that concluded 22 years ago.

'Random noise'

But a special panel of the US Research Council subsequently disputed the evidence of a fourth shot, saying it was simply a random noise recorded about a minute after the shooting.

The congressional investigation concluded in 1978 that President Kennedy was killed by a final bullet from Oswald's rifle.

Oswald was himself shot dead shortly afterwards

But Mr Thomas believes it was the shot from the knoll, seven-tenths of a second earlier, that killed the president.

G Robert Blakey, former chief counsel of the House Committee on Assassinations, welcomed the new findings.

"This is an honest, careful scientific examination of everything we did, with all the appropriate statistical checks," he said.

"We thought there was a 95% chance there was a shot from a grassy knoll. He puts it at 96.3%. Either way, that is beyond reasonable doubt."

Oswald was himself shot dead shortly afterwards by an assassin, Jack Ruby.