In this video, made shortly after the assassination, MacNeil says he entered the TSBD “not more than 4-minutes after the shooting” (beginning around time of 1:02:00).
MacNeil has also said in several interviews that, after he called his office to report the shots, a young black man and another man were reporting their sightings of a man with a rifle to the police. I would assume these were Euins and Brennan. Both of who said they reported their accounts to the police just a few minutes after the shooting. Now, if anyone can help determine the timing of the video in question, it might help us to be able to decide if it is possible that the man approaching the steps is MacNeil.