I'm writing a story and I need certain information regarding the police?

I already know the police scanner codes. I need...well. When dispatch is calling out to a specific squad car how do they introduce it? I'm sure dispatch isn't always like, 'All units...'. So what does dispatch say exactly to a specific squad car to let them know specifically about something? Also. If something were to happen to both police on the case (like if they're injured or dead) and the case is crucial and might lead to a bigger case does the chief put someone else on the case? Thanks. (: And if you know anything else about the whole police/dispatch/chief business it would be great if you could inform me.