[blackbag]

"maybe he is a delivery person"

or maybe he plans his hits to coincide with
similar delivery/ service truck schedules.
Everyone watchin for the truck, he waits till truck is leaving target location then takes his shot. Sits watchin at a distance or leaves in something else, not in a hurry.
Maybe a similar truck in the area is his que.

[RAT Patrol]

It could be that too. Either way, I am sure they are checking what kinds of deliveries these businesses receive. The school probably has vending machines, gets food deliveries, and receives mail and other packages and that's about it.