GZ was a neighborhood watch volunteer and knew who lived in his neighborhood.

TM was suspended from school for an unusually long time for "Being in an area without authorization", which is all the school will reveal about his suspension. (The unusually long suspension suggest he might have been in the school nurses office looking for prescription drugs, perhaps.) TM went to visit his father during that suspension, which is what took him from Miami to Sanford, Florida. It's the fact that GZ had never seen TM before that made him suspicious that he was wanting to break into houses.

This whole tragic story could have all been avoided through communication, GZ communicating to TM why he was following him, or TM communicating to GZ why he was new to the neighborhood. But, that's just not what happened. Instead, there was a fight and GZ shot TM is what fully appears to be self defense.

Video of TM smoking pot, or the fact that he was suspended from school, or recently got into trouble for punching a city bus driver weren't allowed into evidence because none of those things have any bearing on the decision the jury had to make, which was whether this was a murder or self defense.

I think it's best to accept the jury verdict of self defense, and just be glad there was no more rioting than there was. This won't be the first or last time that something happens and there isn't enough evidence to prove the defendant's story wrong.