Myopic, are you? You focussed on one aspect, and a rather small one at that. Whether the firearm had been or had not been processed has little to do with what initated the physical confrontation prior to the shooting.
But it does have to do with your contention that the police did a bad job of investigating doesn't it?
In this entire mess, that's the rub. THAT is what needs to be understood.
The neighborhood is reported to be LESS than 50% white, so it would seem unlikely that Zimmerman focused on Martin purely out of some racist animosity. That is, it couldn't have been unusual to see a black man walking down the street in that neighborhood, so that alone shouldn't have been a red flag for Zimmerman.
What did Zimmerman see that made him nervous, that made him track the movements of this (6'2") teen? Was Martin strolling along toward home with purpose and a destination, or was he moving slowly and aimlessly? Was he stopping to peek into parked cars? Did Martin take a "shortcut" across private lawns? Did he look like he was "casing" a house?
WHAT made Zimmerman nervous enough to call the police even before the confrontation ever took place?
One very important thing is missing here: Zimmerman's FULL side of the story.