Double Jeopardy

Just as was true in the Roman Republic, a conviction today can be appealed and reversed, but an acquittal is final and cannot be appealed. As with the Ashe principle discussed in the last section, one justification is that appeal of an acquittal creates too much risk that an innocent defendant will be worn down by the superior resources of the state. A justification from outside the double jeopardy clause is that permitting an appellate court to reverse a jury's acquittal would violate the Sixth Amendment right to trial by jury (this justification does not explain why acquittals by judges are also non-appealable).

While the jury should have the final say in deciding the facts that underlie an acquittal, the bar of prosecution appeal seems less persuasive when the trial judge has made an error that keeps some important fact from the jury. Suppose the trial judge suppressed a confession that was clearly admissible. The jury's acquittal in this situation is based on incomplete information. In 1937 the Supreme Court in Palko v. Connecticut upheld the constitutionality of a state process that permitted the prosecution to obtain a new trial by appealing an acquittal infected by legal errors. The doctrinal framework of Palko was rejected in 1969 in Benton v. Maryland, however, and most commentators believe that the double jeopardy clause does not permit a prosecution appeal even on the ground of legal error.

Appeals are therefore tilted in favor of the defendant. A guilty verdict can be appealed and reversed, but an acquittal, even if clearly wrong, can never be reversed on factual grounds and probably not on any other ground. This is perhaps a fair price to pay to ensure that innocent defendants are not convicted after repeated trials and appeals.