Lead research Cliff Spiegelman stressed, however, that the research doesn't 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 Spiegelman, a Texas A&M statistics professor and 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 U.S. 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 the late forensic chemist Vincent Guinn, who said recovered fragments came from only two bullets. Guinn testified that the bullets Oswald used, Western-Winchester Cartridge Co. 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 Spiegelman and his fellow researchers, who tested 30 of the same type of bullets, found that fragments were not nearly 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 detailing their study, set to be published later this year by the journal "Annals of Applied Statistics." The study is available on the journal's Web site.
"If the assassination fragments are derived from three or more separate bullets, then a second assassin is likely, as the additional bullet would not be attributable to the main suspect, Mr. Oswald," they wrote.
The bullets Spiegelman's team used were from two of only four lots ever produced of the ammunition. The researchers were able to test for more elements than Guinn and used better quality control techniques, Spiegelman said.
Gary Mack, curator of the Sixth Floor Museum in Dallas, which focuses on Kennedy's life and assassination, questioned the study's methods.
"Their study can't answer anything about the assassination," he said. "That's my understanding of it because they didn't test the actual fragments. They tested similar fragments and found that the test itself is flawed."
Conspiracy supporters believe it helps prove that Oswald didn't act alone.
"Is this going to solve the case, create further investigation or change anybody's mind? Probably not, but it supports the contentions of conspiracy researchers all through the years," said Jim Marrs, whose book, "Crossfire: The Plot That Killed Kennedy" was one of two used as the basis for Oliver Stone's conspiracy film "JFK."
Spiegelman advocates for the bullet fragments from the assassination to undergo more rigorous analysis. Further testing of the fragments 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.