The prosecutor could have done an excellent voir dire and the same result could have occurred. One can never really predict what a jury will do once it retires to deliberate. One side could present what most observers in the court room thought was the far better case and yet still lose because the jurors saw the case differently or considered things other than what everyone else considered. Lawyers do their best to pick jurors that will be more sympathetic to their case, but the limited time the lawyer has to ask questions means that they can't get a very in depth picture of the juror. And given the limited peremptory challenges (the ability to kick off a juror without cause) in many jurisdictions the lawyer can only do so much to weed out those he or she suspects might not be favorable for his/her case. In short there is just no way to know on the limited information we have — that the jury acquitted the defendant just on a feeling that the whole process was overblown for a theft charge of $60 — whether the prosecutor did a good voir dire.