With spells. I'm going with runes so it will likely be Kano to be very visible (it counter acts the invisibility rune dagaz but also helps make people noticable as well as the wunjuo. Perhaps some ISA to make them slow down and also to make them slip up. I rarely cast halgalaz as I hear it can come back on you - one of the runes notorious for that, but if the person continues I'll throw it at them.
Anybody got anything else? I hear two people are in custody but I question that. This sounds like something where they shooter would go down shooting and the cops would be taking him out, no arresting him. He's shot 11 cops so far.