Factual error: After the hitman Joe shoots Ed in his office and is placing the gun in Ed's hand, it discharges and shoots a hole in the wall. The appearance of the wallpaper around the hole makes it look more like an exit hole than an entrance hole.
Factual error: When the two detectives are looking at the car wreck, one says "We found these in the back seat of the Caddy." The car is actually a Lincoln.
Factual error: The Taurus that crashes into the limo at the beginning of the movie is seen soaring down the road with lots of people in it, two of them hanging out of the sunroof. At the moment the crash is shown, there are no people out of the sunroof - as a matter of fact there is only one person in the car.
Answer: There is no one right answer. See http://film.guardian.co.uk/features/featurepages/0,4120,634856,00.html for some theories from movie critics.
jle