Tool.
There are a lot of pics out there showing the U-shape cut on back of head happens to match the unique butt shape of that keltec he was carrying.
He took college courses on self-defense... dude knows the law VERY well... probably had the sense to crack his own head in the 2 minutes standing in the dark with a kid as he bleeds out.
IF this was a well-planned execution... Well, there would be NO BETTER PREPARED MAN for it than zimmerman. I mean, police training, urge to chase bad guys, hates a=holes, calls 911, creates the fight, falls to the bottom despite 500 hours of grappling training and smaller person... screams for help, shoots in heart, and has a story full of holes caused by changes he made to match the self-defense statute in Florida.
makes you wonder. IF he was going to plan and do this, a dude with his history of shoving cops, beating women, and preparing for this... well, you could find no better prepared man to pull off such an execution