"Does this take into account that LHO was one of the worst sharpshooters that ever got out of the military? Or the fact that it was not possible for a human to run down that many flights of stairs to escape the building in the alotted time of the assassination?"
No need: various reenactments (available on various cable channels) have shown that a marksman of LHO's skill could do the job, and that a moderate pace going down the stairs (and walking to the other shooting he did that day) was well within reason and the timeline.
But it doesn't matter: like aliens, and ghosts, and whatnot, people won't let the facts get in the way of a good conspiracy. They'll just claim the fact collectors are part of the coverup.
That's why the Mars pictures are so fun: folks who previously saw the Face on Mars, but had their fun spoiled by higher res photos now complain that NASA is hiding the truth. Then they use other NASA photos to "prove" that there is/was an alien presence on Mars. Mars is like a Rorshach test for these people.