Ah, because the shot can go high or low based on distance, and it's hard to judge exactly, but it won't go left or right without wind. Makes sense.
I just dont think you could head shoot someone from one skyscraper to another with a 308. Not with all the winds and everything.
Especially not with the thick glass high rise windows have.
Now, if the guy had used a 50 cal sniper rifle, that's a different story entirely.