"Although more than a hundred policemen and newsmen were present in the basement of police headquarters during the 10 minutes before the shooting of Oswald, none has been found who definitely observed Jack Ruby's entry into the basement. After considering all the evidence, the Commission has concluded that Ruby entered the basement unaided, probably via the Main Street ramp, and no more than 3 minutes before the shooting of Oswald.
Ruby's account of how he entered the basement by the Main Street ramp merits consideration in determining his means of entry. Three Dallas policemen testified that approximately 80 minutes after his arrest, Ruby told them that he had walked to the top of the Main Street ramp from the nearby Western Union office and that he walked down the ramp at the time the police car driven by Lieutenant Pierce emerged into Main Street. This information did not come to light immediately because the policemen did not report it to their superiors until some days later. Ruby refused to discuss his means of entry in interrogations with other investigators later on the day of his arrest. Thereafter, in a lengthy interview on December 21 and in a sworn deposition taken after his trial, Ruby gave the same explanation he had given to the three policemen.
The Commission has been able to establish with precision the time of certain events leading up to the. shooting. Minutes before Oswald appeared in the basement, Ruby was in the Western Union office located on the same block of Main Street some 350 feet from the top of the Main Street ramp. The time stamp on a money order which he sent and on the receipt found in his pocket establish that the order was accepted for transmission at almost exactly 11:17 a.m. Ruby was then observed to depart the office walking in the direction of the police building. Video tapes taken without interruption before the shooting establish that Lieutenant Pierce's car cleared the crowd at the foot of the ramp 55 seconds before the shooting. They also show Ruby standing at the foot of the ramp on the Main Street side before the shooting. (See Commission Exhibit No. 2635, p. 220.) The shooting occurred very close to 11:21 a.m. This time has been established by observing the time on a clock appearing in motion pictures
[Report Of The President's Commission On The Assassination Of President Kennedy (1964)]