I was skeptical all along that the prosecutor in the George Zimmerman trial had sufficient evidence to charge murder two. (Here is my post about some of the PR issues arising from the matter.) Dan Markel, at Prawfsblawg, expressed serious doubts a while back and it now appears that the prosecutor has even less evidence than we all had imagined. The prosecutor is ethically required to keep re-evaluating whether the prosecution is justified as the case develops.
The trial judge has now excluded the technical evidence the prosecutor wanted to admit to prove that screaming heard on the taped phone call was the deceased Trayvon Martin. (NPR) Criminal law is not my forte but the murder two charges seem to me to be clearly beyond what an ethical prosecutor should bring.
UPDATE: As the trial nears its conclusion, my concerns about the murder two charge seem even stronger. The proseuctor's office avoided a grand jury so that they could bring a charge that was political. I realize that, as suggested in the comment below, such behavior may rarely be the subject of discipine against the prosecutors in the real world. That's unfortunate.