Once in a great while, a prosecutor unhappy with a judge’s rulings might be tempted to boycott a trial. Perhaps he or she figures that an appellate court will later set matters right by reversing the trial judge. But, particularly after the Supreme Court’s decision in Martinez v. Illinois, this decision would be a huge windfall to the defendant. (572 U.S. ___ (2014).)
In Martinez, a prosecutor who had received several continuances so that law enforcement could locate crucial witnesses decided to boycott trial. That's because the judge refused to grant yet another extension of time. The jury had already been sworn in, but the prosecutor refused to give an opening statement or present any evidence. As a result, the judge granted the defense’s motion for a finding of not guilty.
The Supreme Court explained that jeopardy attaches once the jury has been sworn in. Trials can occasionally end in ways that allow for retrial (for example, a hung jury). But if the judge, before letting the jury decide the case, decides that there is insufficient evidence for a conviction, then there has been an acquittal that the prosecution cannot appeal. (See Acquittals by Judges in Jury Trials.)
Since the prosecution in Martinez presented no evidence, the trial judge found insufficient evidence for a conviction. That constituted an acquittal, the Court said, and was final.
The Supreme Court explained 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. But, as it was, the prosecution was out of luck.