Murder, pure and simply is the responsibility of the murderer. All the more obvious in the case of the sniper.
Another approach might be to get him upset at an appropriate time, mass the police response and react that much quickly when he flies off the handle.
Moose now speaking...2 points
1)They've received a communication and will be responding soon.
2) Postscript threat is "Your children are not safe anywhere, at anytime"