In a sense this is already in effect to the degree that is...necessary, or maybe the word I should use is "appropriate." If anyone who is carrying arms runs into this guy, knows what he looks like and gets a positive ID, and knows what he's done, while it isn't 100% legal to draw on him unless he's presenting an active threat (i.e he has a gun out), no DA in the country would charge you with brandishing. Then from there you say freeze, he reaches for his gun, shit happens.

The problem with deputizing the entire county for a manhunt though is giving people real authority can have some ill effects, and is pretty much guaranteeing mob justice to become a norm again. I'd say we're at the happy medium of "nobody will question you if you do find him, but I'm not going to imbue you with the authority of the state per se."