I'll say that nobody knows 100% of what happened that night. Since they already investigated the matter, I'd also say though that the police know a heck of a lot more about what happened than anybody else outside of Zimmerman. They investigated the shooting and decided that the evidence apparently backed up the version that Zimmerman gave them. Absent any evidence (I repeat, ANY evidence) to make me doubt their competence, I'll believe they made the right call. Whether Martin's parents, or the left, or a percentage of the black population want to make this a political issue is not relevant.
and Zimmerman acted improperly (even if legal).
Can't go along with you there. He was doing what was expected of him in letting the police know about what he considered suspicious activity, in accordance with training received from the police at the neighborhood watch training sessions. The police didn't specifically tell him NOT to follow Martin. They didn't tell him they didn't WANT him to follow Martin. They said they didn't NEED him to do it. With Zimmerman being the one on the scene, having to make the decisions, I'm not going to say that he acted improperly, solely based on how tragic the consequences turned out to be. I wasn't there, so I'm not in a position to judge him guilty of "acting improperly".
There is the error. He did not act in accordance with the training he received in the Neighborhood Watch program. He got out of the vehicle and pursued, that is the crucial and deadly error. That program is explicit about not pursuing a suspect, that was all on Zimmerman. If he avoids that crucial act, we aren’t discussing this.