There are 2 basic elements to every crime: (1) criminal act; and (2) criminal intent. In the murder context, there is also a third element of causation. Thus, in a case like this, the defendant's criminal act and intent must cause the victim's death.
Clearly we have a voluntary act on the part of Zimmerman (i.e. the shooting). But whether we have criminal intent is unclear. With that being said, my concern is that this case might be overcharged. The facts of this case are muddled. Depending on who tells the tale, either Zimmerman followed Trayvon and fatally shot him without any real provocation or Zimmerman stood his ground and acted in self-defense after telling the 911 dispatcher that Trayvon was "coming to check [him] out." But the witness recounts thus far have been contradictory and unsatisfactory. This is certainly not the fault of the witnesses. Critically, however, it seems that no one can testify as to exactly what transpired in the moments preceding the fatal shooting of Trayvon Martin. As a result, it is unclear to me whether George Zimmerman possessed the criminal intent to support a murder charge.
Let me be clear: I think that something terrible has happened here, and I think that George Zimmerman should be held accountable for what he did. But we cannot let our compassion for the victim and his family change the legal definition of murder. That's why I am terrified at the notion that the prosecution might be overcharging. It's Casey Anthony all over again ... the prosecution is putting all of its eggs in the murder basket and neglecting the manslaughter argument.
Of course, the prosecution could have evidence at its disposal that has not been made public information. I certainly hope that that's the case. But if Zimmerman walks - talk about miscarriage of justice. At the same time, if George Zimmerman lacked malice aforethought, which is the required level of criminal intent for murder, then a murder conviction would also be a miscarriage of justice.