If you catch them doing it, and can get to the phone whilst they're doing it, phone up the LAPD and tell them whats happening, if they bullshit about them not being able to do anything, phone them up about 3 mins later, saying 'no need to worry now, i've shot all of them' They will be round in a flash. Might not be the best idea though, but a guy in america did it, that's where the idea comes from.