Without any strong collaborating evidence, they probably should be inadmissible. Plenty of people confess to crimes they had nothing to do with; there are a lot of crazies out there.

"In 1666, Robert Hubert confessed to starting the Great Fire of London by throwing a fire bomb through a bakery window. It was proven during his trial that he had not been in the country until two days after the start of the fire, he was never at any point near the bakery in question, the bakery did not actually have windows, and he was crippled and unable to throw a bomb. Nevertheless, as a foreigner, a Frenchman, and a Catholic, Hubert was a perfect scapegoat. Ever maintaining his guilt, Hubert was brought to trial, found guilty, and duly executed by hanging."

http://en.wikipedia.org/wiki/False_confession#Voluntary_fals...

There's a fine line there to be sure. As a society we'd like to find the true culprit in every crime. Yet we'd also like to allow those caught and truly to be able to confess and save on the resources that requiring a full forensic case as well.

Then the fine line isn't between confession and evidence, it's between justice and vengeance. We're more "satisfied" when the guilty confess as that alleviates some of the need for vengeance. And we do have a need for it since the desire for revenge is often innate and hard to suppress. But that has (rather shouldn't) have any bearing whatsoever on the truth.

If such is true without evidence, it's a hollow truth and has no place in justice, which is punishment for guilt on the basis of truth.

If you are happy to rely on a guilty plea, then the whole thing is ripe for abuse by those with money to just pay/threaten someone to do time for them knowing that the chance of investigation is then minimal. Which happens.

It's a balance between preventing that and not wasting resources preparing a full forensic etc. case for EVERY plea which could be used on other more questionable/difficult cases.

"Western" is an exaggeration -- rather, the common law justice system.

Many European countries, including Sweden, don't have guilty pleas in the American sense. In a Swedish trial, the court must find that the suspect is proven guilty. A confession can be treated as evidence, similar to evidence from witnesses, but just like with a witness the court still has to rule on how credible it is. Except for minor crimes (such as speeding tickets), one can not plead guilty to bypass the trial.

Also, the prosecutor does not have any discretion about what crimes to charge (there is a duty to charge any crime that can be proven). One major consequence is that there is are no plea bargains.

UK: we have some limitations on confession evidence [1]. All formal questioning is recorded.

There is evidence to suggest that people make false confessions even without police 'pressure' [2]

[1] http://www.cps.gov.uk/legal/a_to_c/confession_and_breaches_o...

[2] http://www.theguardian.com/uk/2011/oct/09/false-confessions-...