[Kevin]

I don't see how it could be manslaughter.

If Zimmerman was acting in self defense, he's not guilty.

If he approached Martin and intended only to accost him and they got into a physical altercation in which Martin got the upper hand, that's still self defense (no duty to retreat in Florida), he's not guilty.

If he approached Martin and intended only to accost him and they got into a physical altercation in which he got the upper hand, he then took his sidearm and shot Martin in the heart, he's guilty of murder. In most states premeditation can happen in an instant and it takes deliberation and thought and purpose to pull a gun, aim and shoot, and shooting in the heart shows intent to kill, so he'd be guilty of murder.

If Zimmerman assaulted Martin and the fight went either for Martin or for Zimmeman and Zimmerman shot Martin while committing the battery, that's murder or felony murder.

I just don't see a scenario where manslaughter can happen.