The exact time of the assassination was fixed by the testimony of four witnesses. Special Agent Rufus W. Youngblood observed that the large electric sign clock atop the Texas School Book Depository Building showed the numerals “12:30” as the Vice-Presidential automobile proceeded north on Houston Street, a few seconds before the shots were fired.[C2-141] Just prior to the shooting, David F. Powers, riding in the Secret Service followup car, remarked to Kenneth O’Donnell that it was 12:30 p.m., the time they were due at the Trade Mart.[C2-142] Seconds after the shooting, Roy Kellerman, riding in the front seat of the Presidential limousine, looked at his watch and said “12:30” to the driver, Special Agent Greer.[C2-143] The Dallas police radio log reflects that Chief of Police Curry reported the shooting of the President and issued his initial orders at 12:30 p.m.[C2-144] Speed of the Limousine William Greer, operator of the Presidential limousine, estimated the car’s speed at the time of the first shot as 12 to 15 miles per hour.[C2-145] Other witnesses in the motorcade estimated the speed of the President’s limousine from 7 to 22 miles per hour.[C2-146] A more precise determination has been made from motion pictures taken on the scene by an amateur photographer, Abraham Zapruder. Based on these films, the speed of the President’s automobile is computed at an average speed of 11.2 miles per hour. The car maintained this average speed over a distance of approximately 136 feet immediately preceding the shot which struck the President in the head. While the car traveled this distance, the Zapruder camera ran 152 frames. Since the camera operates at a speed of 18.3 frames per second, it was calculated that the car required 8.3 seconds to cover the 136 feet. This represents a speed of 11.2 miles per hour.[C2-147] In the Presidential Limousine Mrs. John F. Kennedy, on the left of the rear seat of the limousine, looked toward her left and waved to the crowds along the route. Soon after the motorcade turned onto Elm Street, she heard a sound similar to a motorcycle noise and a cry from Governor Connally, which caused her to look to her right. On turning she saw a quizzical look on her husband’s face as he raised his left hand to his throat. Mrs. Kennedy then heard a second shot and saw the President’s skull torn open under the impact of the bullet. As she cradled her mortally wounded husband, Mrs. Kennedy cried, “Oh, my God, they have shot my husband. I love you, Jack.”[C2-148]