Here is what Chaney reportedly told the FBI in 1975:

DPD Chaney's first four statements were that there were only two shots. It takes 12 more years for him to add the additional shot. He was wrong four different times in 1963 but right in 1975?
James Chaney . (11-22-63 interview with KLIF radio, reportedly around 12:45 PM--but not broadcast at that time--"On the first shot we thought it was a motorcycle backfire. I looked to my left and so did President Kennedy, looking back over his left shoulder, and when the second shot struck him in the face then we knew that someone was shooting at the President." (When asked what happened after the President was hit) "He slumped forward in the car. He fell forward into the seat there." (When asked Mrs. Kennedy's reaction) "I don't know. When I seen that he was hit well I went on up ahead to tell Chief Curry's group there that he had been hit there, and we took him on to the hospital from there." (When then asked if he saw where the bullet had come from) "No, all I knew is it come over my right shoulder."
An example of Medias Influence
(Note: some sources have it that Chaney mentioned “a third shot that was fired that (he) did not see hit the President” and that he did see “Governor Connally’s shirt erupt in blood..” in one of his first interviews, but I can not find a primary source for these quotes.)
(Article in the 12-2-63 issue of Newsweek, presumed to be based on an 11-22-63 interview of Chaney at Parkland Hospital by motorcade witness Charles Roberts) (On the first shot) "'I thought it was a backfire,' said Dallas Patrolman James M. Chaney, who was riding a motorcycle 6 feet from the right rear fender of the President's car." The President jerked his head around...Then (came) the second shot and his head exploded in blood..."
(11-22-63 interview with Bill Lord on WFAA television, apparently in the early evening) “I was riding on the right rear fender... We had proceeded west on Elm Street at approximately 15-20 miles an hour. We heard the first shot. I thought it was a motorcycle backfiring and uh I looked back over to my left and also President Kennedy looked back over his left shoulder. Then, the, uh, second shot came, well, then I looked back just in time to see the President struck in the face by the second bullet. He slumped forward into Mrs. Kennedy’s lap, and uh, it was apparent to me that we were being fired upon. I went ahead of the President’s car to inform Chief Curry that the President had been hit. And then he instructed us over the air to take him to Parkland Hospital and he had Parkland Hospital stand by. I went on up ahead of the, to notify the officers that were leading the escort that he had been hit and we're gonna have to move out." (When asked if he saw the person who fired on the President) "No sir, it was back over my right shoulder.” (At the end of the interview, Bill Lord, now back in the studio, adds "This patrolman was so close to the president that following the three shots his uniform was spattered with blood."
(11-23-63 article in the Houston Post) "Dallas Police Motorcycle Officer J. M. Chaney told a Houston Post reporter that he was riding about six feet from the right rear fender of the President's car. He heard two shots that seemed to come over his right shoulder, he said. He said the President turned his face around over his left shoulder to look back after the first shot and was hit by the second shot in the left side of the head. Chaney said he did not know if the first shot hit anybody or not."
Another great example of “Medias Influence”. DPD Chaney never said this at all; Chris Davidson stated it for DPD Chaney.
(11-24-63 article in the Houston Chronicle, posted online by Chris Davidson) "A motorcycle policeman just six feet from President Kennedy when he was hit said the assassin's first shot missed entirely. The second of the three shots felled Kennedy, said patrolman James M. Chaney. He was six feet to the right and front of the President's car, moving about 15 miles an hour while rounding a curve. The shot, said Chaney, came from the sixth floor of a warehouse building about 50 feet or less behind the President's car. From the sixth floor to the President, the bullet traveled about 110 feet, Chaney estimated. Chaney was an infantryman in Europe during World War II, with experience in sharpshooting. 'When the first shot was fired, I thought it was a backfire,' Chaney said. Everyone looked around. The President was looking back over his left shoulder.
A second or two after the first shot, the second shot hit him. 'It was like you hit him in the face with a tomato. Blood went all over the car. DPD Chaney is still referencing the second shot was the headshot. Newsman Chris Davidson completely misses the point.