in theory, there could be a federal criminal case for denial of civil rights - remember, that is what happened to the cops in the Rodney King case. I do not see that happening here and think Zimmerman's lawyer by saying he (Zimmerman) was the victim of racism are trying to poison that well - remember, we have a Black President and a Black Attorney General, and were the feds to step in . . ..
However, the parents still have the right to file a suit for wrongful death.
Several things worth noting about such a suit
1. It is a civil case
2. that means the standard of proof is much lower, preponderance of the evidence. Evidence that does not rise to the level of beyond a reasonable doubt is often more than sufficient to meet this standard. However, the defense would try very hard to argue that at a minimum Martin was partially responsible for what happened which therefore means he or his heirs are not entitled to damages.
3. But, because it is a civil case, the 5th Amendment provision against self-incrimination is not in effect. Zimmerman would be required to submit to questioning by the attorney(s) for the Martin. I do not know the specific legal rules of procedure in Florida, but in theory they could both depose him and question him before the jury. He cannot remain silent, because he is not at this point, having been fully acquitted of all criminal charges under state law, under any jeopardy of self-incrimination.
4. However, if there is a Federal civil rights case even potentially on the horizon, that could delay getting a deposition for just that reason, because such a deposition could be used by federal prosecutors and thus self-incrimination could be considered to apply.
It is not yet over.
What happened is sad, but the real travesty starts with the poor job done by the prosecution and anyone watching the trial had to know that.