People saw someone on the roof in the days before the shooting, so whoever it was would have been able to determine the exact distance for sighting the rifle.
Just go to a range with a 200 yard field and sight the rifle to be dead on at 200 yards or whatever the exact distance was.
At that point the average deer hunter could probably make the shot.
On the roof about to commit murder and a day at the range are really different experiences.
E. Pluribus Unum wrote: “People saw someone on the roof in the days before the shooting, so whoever it was would have been able to determine the exact distance for sighting the rifle.”
Google maps gives you the exact distance without visiting the rooftop.