He might be on foot. But it is certain he has evaluated his target for clear line-of-sight. It might serve law enforcement if they would investigate the crime scenes with attention to direction of fire. They could go back along the line of sight and visit the shooting scene instead of the killing scene. There may be certain similarities among the various blinds the shooter is using.
At the elementary school shooting, we know the cops identified the place where the shots were fired. The note and the tarot card were left there.
Presumably, they also have scent swabs from that location. It might very well be a dog who eventually identifies the sniper.