"A passer-by got up close enough and saw a (boot) pressed against a window.".....
Sooo, the passer-by got closer than the guy putting the parking tickets on the car? Maybe the passer-by was hoping to do more than pass-by,,,if you get my drift.
Hmm. Hercule Poirot might ask, If he drove himself to the Emergency Room and collapsed in his car before he could get out, then what was he doing lying in the back seat?