You're assuming a gun was used at close range. That's not the only option to take someone out.
I believe you're missing my point. It's not about a specific murder weapon.
Watch a bunch of real murder shows on the Murder Channel (investigation discovery?). You'll see a general trend that the forensics catches bad guys because various methods of murder leave prints, claw marks, blood splatter, gun powder, tissue under fingernails, post mortem injuries versus pre-mortem injuries, etc that can contradict what ever story you make the scene appear to be for when the cops get there.
Once contradictions appear of what the scene appears to be and what the evidence says, the cops will dig in deeper and that unravels the plan.
To get away with the crime, you'd need to get the guy killed in a fashion that is consistent with the evidence the cops will find. If the cop sees a straight forward crime scene with no obvious contradictions, they won't inspect deeper. I do not believe this would be a trivial thing to stage without a lot of planning, prep and excellent secrecy.
Take the Trayvon Martin case that [MENTION=9037]Elf Witch[/MENTION] brought up. The shooter claims he was attacked. If there's not obvious evidence supporting his claim, that looks fishy to a cop. If the cop calls in forensics, and they verify that there's no evidence of a scuffle on either party, then the shooter has been caught in a lie.
Like the "Don't talk to cops" video says, once a cop catches a whiff of a lie, their guilt meter goes off and they usually drill in deeper.
I have no idea why Zimmerman was let go. There must be more to what happened in his interview with the police (remember, he was cuffed and hauled in).
For me, taking both parties at face value of how the incident started:
black kid in hoodie coming back from a snack run while talking to GF
hispanic guy keeping a watchful eye on his neighborhood
Ending with an interaction between the 2 and one guy is dead, I'm inclined to think the guy who lived should be in trouble. Because neither party would have been involved in any wrongdoing had they kept their distance (which sounds like Zimmerman initiated contact by approaching the boy). Furthermore, 2 innocent parties who are wary of the other are both going to claim "Standing their ground" Once that happens and neither party was in prior act of engaging in crime, that defense is out the window as feasible. The case should be investigated as 2 men who meet and things escalate into a terrible outcome.
This is why school-aged children insist that "who started it" is important. Because the whole problem stems from an instigator, not the final outcome.