funny little fact you bring up there.
the fact that zimm told the dispatch to have police phone him for his location, rather than meeting them where he told them his truck was parked, tells me that zimm was gonna go out searching for martin, which is exactly what happened.
he hangs up with 911, goes searching for martin, finds him about a minute and a half later, and about a minute after that martin is dead.
not exactly the conduct you would expect from someone with concealed carry, to go out looking for a confrontation. kinda nullifies self defense when you go out looking for someone who is already running away from you.