Mrs. Reid believes that she returned to her desk from the street about 2 minutes after the shooting.[C4-396] Reconstructing her movements, Mrs. Reid ran the distance three times and was timed in 2 minutes by stopwatch.[C4-397] The reconstruction was the minimum time.[C4-398] Accordingly, she probably met Oswald at about 12:32, approximately 30-45 seconds after Oswald’s lunchroom encounter with Baker and Truly. After leaving Mrs. Reid in the front office, Oswald could have gone down the stairs and out the front door by 12:33 p.m.[C4-399]--3 minutes after the shooting. At that time the building had not yet been sealed off by the police. While it was difficult to determine exactly when the police sealed off the building, the earliest estimates would still have permitted Oswald to leave the building by 12:33. One of the police officers assigned to the corner of Elm and Houston Streets for the Presidential motorcade, W.E. Barnett, testified that immediately after the shots he went to the rear of the building to check the fire escape. He then returned to the corner of Elm and Houston where he met a sergeant who instructed him to find out the name of the building. Barnett ran to the building, noted its name, and then returned to the corner.[C4-400] There he was met by a construction worker--in all likelihood Howard Brennan, who was wearing his work helmet.[C4-401] This worker told Barnett that the shots had been fired from a window in the Depository Building, whereupon Barnett posted himself at the front door to make certain that no one left the building. The sergeant did the same thing at the rear of the building.[C4-402] Barnett estimated that approximately 3 minutes elapsed between the time he heard the last of the shots and the time he started guarding the front door. According to Barnett, “there were people going in and out” during this period.[C4-403]