It might be better if we do juries first, since this is a complicated maze of an issue on which I've changed my mind, thanks in no small part to the legend that is Malpoet. Trial by one's peers has a certain symetry in terms of being the judicial equivalent of representative democracy, seen by its supporters as 'the least worst system, apart from all of the others'. Isn't it nice that the butcher and baker can own a stake in the judicial process, even if it's clear cut that they're either ill-equipped to measure guilt beyond a reasonable doubt, or have no interest in following the nuances of the case whatsoever.
What is reasonable doubt anyway? I've heard two basic attempts to define this rather important term, and neither seem adequate. One is basically the measurement of certainty regarding a man's guilt expressed as a percentage, but then this is highly subjective. If we accept that 'beyond a reasonable doubt' stops just short of absolute certainty, then how convinced of the defendant's guilt must one be in order to pass that threshold? Are we talking 85% here? Or 90, 95 or even 99.9%? People will of course reach their wildly varying conclusions on this, and though one might suggest that 15% certainly represents sufficient reasonable doubt for acquittal, the other eleven members of the jury may see the standard somewhat differently.
Then there is the problem of potential jurors who 'just know' instinctively whether or not a defendant is guilty by weighing up body language, making eye contact, whatever. Both of my parents were of this ilk, as is the other half of a friend/contributor to this site. Folk like this are the type who quite clearly want to be on a jury and should therefore be disqualified from being on one. That's before you get near issues such as racism, religious bigotry or homophobia that may cloud the mind of a juror, consciously or otherwise.
I vividly remember as a teenager arguing with my mother after Barry George was sentenced, looking at the evidence (or lack of) and concluding that an innocent man had just been condemned. Her (god honest) response? "You fucking do-gooder. Sometimes you just KNOW the guy in the dock is guilty as hell". Kids, my advice has always been to ignore your parents and do your thing, they're usually talking shit - QED.
Then again, this poses a different question - why the fuck did I continue to support juries, even after that experience? Daz, you fucking moron - just thank god you met Malpoet and saw sense...
Double jeopardy is a different issue entirely, although there is a question that bothers me and I'm yet to formulate a complete answer to - "how can you say that a guilty verdict might be wrong but a not guilty one cannot be?". This is a fair question if one assumes that the right of appeal and the concept of double jeopardy are two sides of the same coin. All I would say for now is that the default status of a defendant (as 'J' rightly points out) is innocent until proven guilty and so it is the job of the prosecution to prove beyond a reasonable doubt (whatever that threshold might be) that they are nailed on, guilty as sin.
What the old system did was ensure that no stone was left unturned as the authorities sought to establish the guilt of the defendant. Presented with only one crack at the person they deem to have done the crime, a team of skillful and dedicated professionals would have to present a watertight case to the court and this means a thorough and diligent job in terms of the gathering and piecing together of evidence. One could argue that it also leads to greater fabrication of evidence and the wheeling out of false 'experts' in order to nail the defendant, and I'd be arrogant to dicount that entirely.
It also ensures that a 'not guilty' verdict actually means something. The relief of being acquitted when one knows they have done nothing wrong essentially derives from the sense that it's finally over. What you have to remember is that when a defendant is found 'not guilty', the authorities almost always believe that a guilty man has 'got off' - why else would they have been on trial in the first place? People can be in the wrong place at the wrong time, or have an argument with someone who rocks up dead shortly afterwards, providing ample circumstancial evidence that points towards their guilt. All it takes is a mysterious eyewitness to turn up out of nowhere, or an alibi to be withdrawn by a friend who is no longer so, and the man they believed 'whodunnit' all along is back in the dock.
Anyone believing this to be far-fetched should ask - did Jeffrey Archer's alibi go to jail when he admitted perjury? No, deals were done, as they will always be.
And, please, please read 'the Monster of Florence' if you want a realistic picture of the lengths that the authorities will go to in order to nail someone, anyone.
What is the justice system there to do? It is surely there to convict the guilty and acquit the innocent, but we should be mindful that no justice system on earth will get it right 100% of the time. If it did, then perhaps the baying mob supporting the death penalty could have their wish. What's the real choice? Perhaps it's between a man guilty of murder being locked up solely for perjury, or a man guilty of nothing being harassed to an early grave by a state that is convinced of his guilt on the basis of flimsy evidence. As someone with a natural mistrust of the state, I know which of these menaces I see as the greater threat. Take care and I'll catch you soon.