New testing on the type of ammunition used in the 1963 assassination of President John F. Kennedy raises questions about whether Lee Harvey Oswald acted alone, a study claims.
But Cliff Spiegelman, lead researcher on a study by Texas A&M University, stressed that the findings do not necessarily support conspiracy theorists, who for decades have doubted Oswald was the lone gunman.
"We're not saying there was a conspiracy. All we're saying is the evidence that was presented as a slam dunk for a single shooter is not a slam dunk," said Prof Spiegelman, an expert in bullet-lead analysis.
The Warren Commission concluded in 1964 that Oswald fired three shots at Kennedy's motorcade from the Texas School Book Depository in Dallas.
The US House Select Committee on Assassinations agreed in 1979 and found that the two bullets that hit Kennedy came from Oswald's rifle.
The committee's findings were based in part on the testimony of former chemist Vincent Guinn, who said recovered fragments came from only two bullets.
Mr Guinn testified that the bullets Oswald used, Western-Winchester Cartridge Mannlicher-Carcano bullets, were unique and that it would be possible to distinguish one from another even if they both came from the same box.
But Mr Spiegelman and his fellow researchers, who tested 30 of the same type of bullets, found that fragments were not so rare, and that bullets within the same box could match one another.
One of the test bullets also matched one or more of the assassination fragments.
"This finding means that the bullet fragments from the assassination that match could have come from three or more separate bullets," the researchers wrote in a paper set to be published later this year by the journal Annals of Applied Statistics.
Prof Spiegelman advocates for the bullet fragments from the assassination to undergo more rigorous analysis. That would be up to the National Archives and Records Administration, the legal custodian of the projectiles and other evidence used by the Warren Commission.
The last time the fragments were tested was in 1999. The examination was inconclusive.
AP