Retrials and double jeopardy: when can someone be tried twice?

Most legal systems hold that a person should not face prosecution twice for the same offence. The principle is known as double jeopardy, and it exists to stop the state from using its far greater resources to wear a defendant down until it gets the result it wants. It is not absolute, though. A retrial may be allowed in some circumstances, and these differ from country to country.

What double jeopardy means

The rule has two parts. The first protects a person who has been acquitted, meaning found not guilty, from being prosecuted again for the same offence. The second protects a person who has been convicted from being punished twice for the same conduct. The Latin phrase ne bis in idem, "not twice for the same thing", is often used in civil law countries and in international law.

The protection is tied to a final outcome. A trial that ends without a verdict, or a conviction that is later set aside on appeal, does not usually count as a final decision in the defendant's favour. That distinction explains most of the situations in which a second trial is lawful.

When a retrial is usually allowed

After a mistrial or hung jury

If a jury cannot reach a verdict, or a trial is halted because of a serious procedural problem, there is no acquittal or conviction. The prosecution can normally ask for a fresh trial. In the United States, a defendant who asks for a mistrial generally cannot then rely on double jeopardy to block a new trial, with a narrow exception where prosecutors deliberately provoked the request.

After a quashed conviction

When an appeal court sets aside a guilty verdict, the case is sometimes sent back for a new trial. In England and Wales, the Court of Appeal can order a retrial when it quashes a conviction if it considers that the interests of justice require one. Courts weigh the seriousness of the offence, the time that has passed and whether a fair trial is still possible. If the conviction was quashed because the evidence was legally insufficient, many systems, including that of the United States, bar a second attempt.

After a tainted acquittal

Some jurisdictions allow an acquittal to be challenged where it was obtained by interference, such as intimidation of a juror or witness. England and Wales has a specific procedure for this, and the High Court must be satisfied that the acquittal was tainted.

Retrial after an acquittal on new evidence

The most debated exception concerns people who were acquitted and are later said to be guilty. In England and Wales, the Criminal Justice Act 2003 changed the traditional rule for a list of serious offences, including murder, manslaughter and rape. The prosecution can apply to the Court of Appeal to quash an acquittal if there is new evidence that is both reliable and compelling, and if a retrial is in the interests of justice. The Director of Public Prosecutions must consent before an application is made.

Scotland has its own legislation, the Double Jeopardy (Scotland) Act 2011, which allows a second prosecution in limited circumstances, including where new evidence emerges or where an earlier acquittal was tainted. Ireland and some other common law countries have adopted comparable reforms.

Supporters argue that advances such as DNA analysis can make a verdict look unsafe years later, and that victims' families should not be denied a second look. Critics respond that a final acquittal is a cornerstone of fairness and that reopening it risks eroding public confidence in the finality of verdicts.

How other systems approach it

Jurisdiction	General position
England and Wales	Retrial after acquittal allow