In the U.S. Supreme Court case of the State of Michigan versus Lamar Evans, the facts were as follows:
After the prosecution rested its case at Lamar Evans' arson trial, the judge granted Evans' motion for a directed verdict of acquittal, concluding that the prosecutor had failed to prove that the burned building was not a dwelling, a fact the judge mistakenly believed was an “element” of the crime. The prosecutor appealed, and the Michigan Supreme Court reversed Evans' acquittal, ruling that a directed verdict based on an error of law that did not resolve a factual element of the charged crime was not an acquittal for double jeopardy purposes.
However, the U.S. Supreme Court disagreed and ruled that the Double Jeopardy Clause contained in the U.S. Constitution did, in fact, prevent Mr. Evans from being tried once again. The Court said that being tried a second time following a judge's acquittal is barred, even if the acquittal is based upon an error such as an incorrect decision to exclude evidence, or a mistaken understanding of what evidence is sufficient to sustain a conviction, or a misconstruction of the statute defining the requirements to convict. Most relevant in Mr. Evans' case, an acquittal encompasses any ruling that the prosecution's proof is insufficient to establish criminal liability for a crime.
In contrast to procedural rulings, which lead to dismissals or mistrials on a basis unrelated to factual guilt or innocence, acquittals are substantive rulings that conclude proceedings absolutely and thus raise significant double jeopardy concerns. Here, the trial judge clearly evaluated the prosecutor's evidence and determined that it was legally insufficient to sustain a conviction. Evans' acquittal was the product of an erroneous interpretation of the law, but that error affects only the accuracy of the determination to acquit, not its essential character.