If Oswald needed to walk briskly without wiping off his prints then any extra time would have quickened his pace. There were no smeared prints on the rifle, they were wiped off clean or were never there in the 1st place. Since I don't believe Oswald smuggled the rifle into the TSBD in a paper bag or reassembled it or fired it or planted it, my guess is the latter. Seems more probable to me. Conspirators would never have relied on the patsy to stage the crime scene and take the shots and ditch the rifle and leave behind 3 hulls on the floor in a tight group near the SN window. That was Fritz's job. The actual shooter used a more reliable weapon that resembled a Carcano, such as a Mauser.
The shells weren't "left" by anybody in a tight group of three by the window.
Two of them were about a foot apart from each other by the window, and the other one was several feet away, on the other side of the Sniper's Lair.
-- MWT