[StevieB]

If this is a commuter bus and the driver was shot with the door open, then somebody must have been standing at that bus stop for him to pull up and open the door. An accomplice?

This could be a schedule coordination stop. The park close to where I live in Pasadena (left coast) is along side the street where one bus company starts its local routes. Buses are often there for a few minutes, waiting to start their run at their scheduled time. It's quite common for the drivers to get out of their bus and walk around a bit or sit on the benches at the edge of the park.

[livius]

"This could be a schedule coordination stop.

Very possible. In that case, we have more evidence that the shooter prepares his sites carefully.