[Patrick C]

IMO the location is such that the view could be blocked or somewhat blocked by bystanders - the assassin would have had no way of knowing how many people would turn up. You are also looking at shooting past the 2 SS guys and the Connallys not to mention the glass partition (I am not sure how extensive this was or if it was fully deployed). Above and high is a better location IMO.

That said I accept that one could be trapped inside a building with only one set of stairs....unless one worked there in the first place......