LIVERMORE -- It's been the subject of numerous arguments, books and a major Hollywood movie and now scientists at Lawrence Livermore Laboratory have turned up the heat again on just who assassinated President John F. Kennedy.

The researchers say metallurgical chemical "fingerprints" on the bullets that killed the president and wounded then Texas Governor John Connally may have been misinterpreted and that the government's crucial "single gunman theory" has been thrown into doubt.

"It basically shatters what some people call the best physical evidence around," chemist Pat Grant, director of the lab's highly respected Forensic Science Center told the San Jose Mercury News.

Grant and Lab metallurgist Erik Randich found that the chemical "fingerprints" used to identify which bullets the fragments came from were not quite the "smoking gun" as thought pointing to Lee Harvey Oswald as the lone gunman.

The FBI used five bullet fragments recovered from the limousine, Connally's body, the president's brain and from a stretcher for its initial tests using what is known as "neutron activation" analysis.

Those tests proved inconclusive, but later tests by chemist Vincent Guinn -- a renowned specialist in neutron activation -- on the bullet lead pointed directly at Oswald. Guinn said the fragments came from just two bullets -- both of which came from Oswald's Russian-manufactured rifle.

Randich said the Lawrence Livermore tests came to a different result.

"We don't know if there were two bullets," said Randich. "There could have been two bullets, but the lead composition data shows there could be anywhere from one to five bullets."