"There has never been anything to indicate positively that anybody else was involved," Robert Frazier, the FBI's lead firearms and ballistics examiner at the time of the shooting 50 years ago, said.
Frazier, now 94, said he was at work at FBI headquarters when Kennedy was shot Nov. 22, 1963.
The chief of the FBI laboratory called in Frazier and two other examiners after learning of the assassination.
"He said, 'I want each of you men to make separate comparisons and examinations, and then compare your notes and see if they agree,'" Frazier said.
Frazier gathered evidence from the presidential limousine, which had been flown back to Washington from Dallas.
"We examined that car very thoroughly that same night," Frazier said.
Frazier worked nonstop for days, the FBI said in its release.
He stayed immersed in the investigation as it progressed and traveled to Dallas to stand in the same sixth floor window where Harvey Lee Oswald stood.
"We re-enacted the entire thing very, very carefully," he said. "I stood up there and we took Oswald's rifle, with the scope on it, and set it up."
Frazier, who also testified before the Warren Commission several times, said looking back on the event still makes him emotional.
"It was a sad situation," he said. "Just remembering that it was Kennedy and what a personality he had. ... It was a terrible, terrible thing."