The Problems with Double Jeopardy
1. Criminals Walk
Even though we do not know which of those the state would like to re-prosecute are guilty and which are actually innocent, it would be extremely naive to believe that no felons slip though the cracks. Even defenders of the double jeopardy law admit that "the price to pay" is the occasional malefactor escaping justice.
2. The Rule of Law
It is an important part of the judicial system that impartiality exists in all civil and criminal procedures. The court looks at both sides with equal favour. The symbol of justice in most English speaking democratic countries is Justitia, the Roman goddess of justice, holding the sword and scales while being blindfolded. The blindfold implies that she is not to be influenced by the appearance or circumstances of any one side. As one adage of the Rule of Law prescribes, "all people are equal under the law". After a criminal conviction the defendant always has an ongoing fundamental right to appeal his or her conviction. This is as is it should be. It therefore seems highly questionable to hold as a principle that one party to a judicially convened court hearing always has a right to appeal the decision made, but the other party only does in limited circumstances.
3. Not just done, but be seen to be done.
It is one thing for investigating authorities not to have any leads as to who may have committed a recent crime. It is quite another for them to have full confidence in knowing who the perpetrator is, but yet to be hamstrung in most instances by an anachronistic centuries old law from any further prosecution.
"... it is not merely of some importance but is of fundamental importance that justice should not only be done, but should manifestly and undoubtedly be seen to be done."
Lord Chief Justice Hewart in R v Sussex Justices Ex parte McCarthy  1KB 256 at 259
4. Respect for the Law
Possibly the most important bulwark of any criminal justice system is our confidence in it. This confidence can only be shaken whenever we hear the term "getting off on a technicality": those using the rules to their advantage in an exploitation of inadequate contemporary evidence, perjury or judicial errors of law to evade ultimately answering for their crimes.
5. Unequal pressure on judicial decisions.
As legal scholar Larry Laudan has held, it would seem reasonable to suppose that trial judges would prefer not to have higher courts reverse too many of the decisions they make during their trials. A judge whose decisions are regularly overturned on appeal probably will be perceived by his peers as less than fully competent. Given this, it becomes significant that virtually no trial rulings made favouring the defendant will be appealed (as nothing will come of it) but that rulings favouring the prosecution will obviously be given serious consideration if it will give the defence an opportunity to appeal a conviction.
This is not to imply that all judicial decisions are driven by craven self interest where otherwise the decision would be clear in any given area. However many trials involve motions calling for rulings that are close calls or borderline cases, where a plausible argument can be made for ruling one way or the other. In those circumstances would it not be a surprise to find a pattern of judicial rulings in favour of the defendant and, not coincidentally, of the sort that would seldom be overruled on appeal?
Laudan, Larry, Truth, Error, and Criminal Law: An Essay in Legal Epistemology, Cambridge University Press, New York, 2006, p.205.
6. The Law is not a Game
Most people do not believe justice should be viewed as a game where if one plays it correctly and manages to carry the ball a certain distance, ducking and diving so as not to be tackled, there then will be goal posts of sanctuary from further prosecution.
7. Sanctuary for Criminals?
It seems incredible that in the twenty-first century, society should maintain a system in which people highly suspected of committing crimes are able, due to technical reasons, to walk freely amongst us. Unless society is getting something substantial in return, how can anything justify state sanctioned immunity for criminal activities.