The Supreme Court's decision in Martinez v. Illinois establishes that prosecutors who decide not to participate in criminal trials have to live with the resulting acquittals. (572 U.S. ___ (2014).)
In Martinez, the prosecution received four continuances so that it could locate the primary witnesses in the case. These continuances pushed the case back approximately ten months. The judge refused to grant another continuance to find the witnesses. After the jury had been selected and sworn in, the prosecutor announced, “[T]he State will not be participating in the trial.”
The prosecutor refused to give an opening statement or present any evidence. The judge granted the defense’s motion for a directed verdict of not guilty. The state appealed all the way up to the U.S. Supreme Court.
The Court explained that jeopardy attaches once the jury has been sworn in. Although trials can occasionally end in ways that allow for retrial (for example, a hung jury), the Court said that the finding that there was insufficient evidence for a conviction constituted an acquittal that could not be appealed. (For information about the effect of a judge's finding of insufficient evidence after the jury has returned a verdict, see Acquittals by Judges in Jury Trials.)
Since the prosecution presented no evidence, the judge found insufficient evidence for a conviction. That insufficiency equaled an unappealable acquittal by the judge.
The Court therefore held that the acquittal was final. It said that the prosecution should have dismissed the case before the jury had been sworn. Then the double jeopardy clause wouldn’t have barred another prosecution of the defendant.