On 22nd November, 1963, Jean Hill, a Dallas schoolteacher, watched the motorcade of President John F. Kennedy from the grassy knoll facing the Texas School Depository Building. Hill and her friend, Mary Moorman were only a few feet away from President John F. Kennedy when he was shot. Hill thought the shots had come from behind her on the grassy knoll and as soon as the firing stopped she ran towards the wooden fence in an attempt to find the gunman. However, Hill was arrested by two policemen and taken into custody.
The vast majority of witnesses in the Dealey Plaza on that day claimed that shots came from two directions: the Texas Book Depository and the Grassy Knoll. The behaviour of the police to the shooting is also very interesting. Film of the Dealey Plaza shows that within seconds of the shots being fired several police charged up the grassy knoll. A few minutes later there were over 50 policemen searching the grassy knoll area and the railroad parking lot that was situated just behind it. This was a far larger number than went into the Texas Book Depository.
In their book The Man on the Grassy Knoll, John R. Craig and Philip A. Rogers claimed that Charles Harrelson and Charles Rogers were the two gunman behind the picket fence on the Grassy Knoll. It was also claimed that Harrelson and Rogers were two of the tramps arrested in Dealey Plaza on 22nd November, 1963.
In 1978 the House Select Committee on Assassinations ordered a fresh investigation of Dallas Police records. In March of that year they discovered a trunk that had been in the possession of the former intelligence director of the department. This included a dictabelt recording of transmissions by police on the day of the assassination. The House Select Committee on Assassinations commissioned two prominent acoustical experts (Dr. James Barger and Dr. Mark Weiss) to study the tape. They concluded that four shots were fired at President John F. Kennedy. The gap between the first and second shots was 1.66 seconds. The third shot took place 7.49 seconds later. The gap between this and the final shot was only 0.44 seconds. It was clear that the third and fourth shots could not have been fired gun.
After establishing where the police motorcycle that made the recording was at the time of the shooting, Barger and Weiss concluded that "with a probability of 95% or better" the third shot was fired from the grassy knoll. They were even able to state that the firing position was behind the picket fence, eight feet west of the corner. This was the very spot where S. M. Holland had claimed he has seen a puff of smoke after he had heard shots on the day Kennedy was killed. It was also the same spot where Phillip Willis' photograph appeared to show, according to computer analysis, "an adult person" standing behind a fence.