The killer(s)appear to be pretty smart. To smart to be driving a white van around anymore.
The killer may not even be trying to leave the crime area anymore. If these shopping centers are near motels, he could easily take out a romm, do his killing, walk back to his room and spend the night watching the local news.
A little theory I've been throwing around... It is possible that he/they spent the last few days of no sniper shootings re-painting their vehicles.