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In defence of the “double jeopardy” rule

James Hammerton

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Why have the double jeopardy rule?
Why can't the prosecution appeal when the defence can?
Doesn't the double jeopardy rule let the guilty walk free?
Surely we can make an exception for serious cases, such as murder,
       where there is compelling evidence of guilt subsequent to acquittal?

A possible exception?

About the author


The double jeopardy rule in UK law states that you cannot be tried for the same crime twice. It is a rule that dates dates back to the 12th century under common law.

Some people may find this rule a bit odd. After all, if new evidence turns up that suggests the defendant acquitted in a trial was in fact guilty of the crime for which he was being tried, then the rule means that person cannot be prosecuted.

During March 2001, in the UK, a Law Commission report recommended for murder cases, that if there is compelling new evidence, a case could be retried and thus end the double jeopardy rule in murder cases. The Labour government indicated that it would bring in legislation to give effect to this proposal in the next parliamentary session.

It is the purpose of this essay to defend the double jeopardy rule, which I regard as a fundamental cornerstone of the British justice system, the undermining of which will lead to innocent people being harassed and jailed and to those who do commit crime walking free.

Why have the double jeopardy rule?

There are a number of reasons for the double jeopardy rule:

  1. The state has far more power to investigate and dig up evidence than an individual.

    This causes an asymmetry when an individual is prosecuted for an alleged crime. The individual will not have the resources to go out and look for the evidence that clears him and anyway, from the point of being charged, may be held in custody whilst he waits for his trial. Thus, the individual’s ability to construct a defence against a charge is quite limited.

    It is for this reason that the principle that you are innocent until proven guilty has informed the development of many legal systems. Allowing repeated trials of the same person for the same offence skews an already imbalanced situation even further in the state’s favour.

    We know that the justice system is fallible. Therefore we know that, even if evidence is not really strong enough to convict, this may still happen. Thus repeated trials of the same person for the same offence will increase the probability of wrongful conviction. In murder cases, this means the guilty party will walk free. Thus, both innocent people will suffer and the perpetrators are free to offend again.

  2. Removing the double jeopardy rule opens up the possibility of the state harassing an individual with repeated prosecutions for the same crime.

    If the state can prosecute someone repeatedly for the same crime, then this makes the option of politically motivated prosecutions more attractive as a means of harassing an individual whom the state does not like or of whom they are suspicious. Since the state would determine the hurdle to be passed for a repeat prosecution, and also has considerable powers to dig up (or even invent) dirt, the situation becomes heavily loaded in the state’s favour.

  3. Removing the double jeopardy rule means that the innocent accused can never rest easy.

    It is quite possible for an innocent person to be accused of a crime and, as a result, they come to trial to trial. If the double jeopardy rule goes then, after acquittal, an innocent person cannot rest easy in the knowledge that no further prosecution can be brought for that accusation and that they can get on with their life, without worrying about a further trial for that crime.

  4. The double jeopardy rule encourages the prosecution to make as strong a case as it can manage.

    If there is only one chance for convicting a criminal, the prosecution are under strong pressure to make the best case they can for convicting the defendant.

    If there is the option of trying again should the conviction fail, then when a crime is being investigated, once the police believe they’ve got their man, there is no pressure to investigate further to ensure the strongest possible case is presented rather than one they think will be merely adequate.

    This will reduce the quality of the prosecution cases and the quality of police investigations, increasing the risk of catching and even convicting the wrong man. Further, even when the authorities have the right man, the chances of an acquittal will be increased, resulting in the accused going free; at least until the police find new evidence and persuade the courts to allow the case to be tried again.

    Thus not only would more innocent people be jailed, but more guilty people may go free as well as a result of removing the double jeopardy rule.

  5. Retrials after an acquittal may undermine the presumption of innocence.

    Another problem with allowing a retrial after an acquittal lies in preserving the presumption of innocence. For example, if the men accused of the murder of Steven Lawrence were to be tried again for that crime, it would be well nigh impossible to find a jury that was not aware of the media coverage of the original trial and, therefore, who may be biased against the defendants.

    If the jury knows they are judging a retrial where what a judge has found to be “compelling”, “new” evidence is available, the jury may decide that they cannot judge that it wasn’t compelling. Yet had the evidence been presented at the original trial, there is no guarantee it would have led to conviction. It is also likely that a retrial will become a cause celebre, with a great deal of political and public pressure for a conviction regardless of the strength of the evidence.

I believe these reasons give strong support for the retention of the double jeopardy rule on grounds of civil liberties, justice and effective crime fighting. The rule was not placed into the legal system without good reason, and certainly should not be abolished without better reason.

Why can’t the prosecution appeal when the defence can?

Some may say that it is unfair that the defence can appeal a conviction when the prosecution cannot appeal an acquittal. Even if this were true, the reasons given above would, in my opinion, outweigh this consideration. However it is not unfair; indeed, the right of appeal on the part of a defendant derives directly from the principle that the innocent should not be punished unless proven guilty of a crime. A right of appeal against an acquittal cannot be so derived.

Doesn’t the double jeopardy rule let the guilty walk free?

In some circumstances, yes it may, simply because the courts are fallible. However as we have seen above, removing the rule may cause more guilty people to walk free, due to a decline in the quality of the investigations and prosecutions (leading to fewer criminals being caught and convicted), caused by the reduced pressure to present the strongest possible case at the first trial for each offence..

This is not a simple case of balancing the risk of jailing innocent people in a repeated prosecution for a crime against letting guilty people walk free through not being allowed to mount a second prosecution. Anyone presenting it in those terms is failing to take into account the factors mentioned earlier.

It should also be mentioned that, where someone makes a full confession after being acquitted, there is the option of pursuing a perjury charge against them; so it is not as if there is no sanction available should someone be wrongly acquitted, and then they flaunt the fact that they were able to get away with a crime.

Surely we can make an exception for serious cases, such as murder, where there is compelling evidence of guilt subsequent to acquittal?

If anything, in a serious case, where the consequences of a wrongful conviction or a wrongful acquittal are serious, the case for an exception to be made is weakest. With serious crimes, it is most important that an investigation and trial be performed with utmost care and thoroughness—mistakes could cost lives and lead to innocent people being jailed for many years. Allowing a repeat trial in such circumstances would lead to an incentive to hold back evidence, or lines of inquiry, for a retrial.

Thus the double jeopardy rule is even more important than normal in such cases, as it puts pressure on the prosecution and the investigators of a crime to do their jobs to the best of their abilities, because they will not have a second chance.

A possible exception?

Through discussing double jeopardy on usenet, it occurred to me that some of the concerns raised about removing the double jeopardy rule can be addressed if a new prosecution is allowed only when the new evidence could not possibly have been presented at the original trial, e.g. because the technology that uncovered the evidence was not available at the original trial.

This proposal would ensure that the incentive to present the strongest case at the original trial would remain—there would be no reason to hold back evidence or lines of inquiry for a possible retrial. It does not address all the concerns raised, e.g. the threat of a retrial hanging over the innocent accused’s head, but it would acknowledge those who argue that when new technology is developed we should be able to do a retrial, without increasing the risk of a lower standard of evidence and more wrongful convictions and acquittals.

However, there is still a problem left: namely that of preserving the presumption of innocence, as decribed in point 5 above. In any retrial involving new evidence, ensuring that no-one on the jury was aware of the original trial, or is aware that the trial they’re judging is a retrial, will be virtually impossible with high-profile cases and may be very difficult otherwise. This consideration, along with the ongoing trend in attacking civil liberties, makes me very reluctant to remove the double jeopardy rule, even in such a rigourously tested manner, lest it become the first stage in abolishing the rule outright or otherwise leads to injustice.


That a few guilty people may walk free because of double jeopardy is, in my humble opinion, a small price to ensure that crimes are investigated properly and that prosecutions are conducted to the best of the abilities of the people involved; and thus to make sure that, as far as possible, justice is done, both in terms of catching those committing crimes and ensuring the innocent are not wrongly imprisoned.

About the author

James Hammerton is a computer scientist with a long standing interest in politics.


This article is copyright. You may distribute it freely so long as you acknowledge my authorship of it.
James Hammerton, 2002





© and James Hammerton, 2002 (9 december)

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