first off DNA testing is not 100%...
100% would mean that it is indisputable, nobody else in the world would have a matching gene, (you said in your own post that the chance of a false positive is something like 1 in 5000 or 1 in 10,000.
perhaps you need a better definition of 100% accurate, I'm not sure I can provide on, certinaly 1 in 5000 is not 100%
Genes run in families so there is a good chance that you will have some matching DNA as say your brother or father or mother /kids etc. even quite distant relative can have a simillar or even exact part of a DNA sequence.
If you've ever seen a DNA test you'll realise that the test could not possibly differentiate between all the diferent people on earth, there siply isn't the resolution in the test equipment to find enough difference to accuratly identify everyone on earth.
fingerprints are also not entierly uniquie, certinaly not in the way they are detected, physically there is a very finite amount of fingerprint patterns that there can be, (thats why they take all 8 fingers and both thumbs -to reduce the possibility of a flase positive), I was once told it is a statistical certainty that you will share the same finger print pattern with at least 4 other people, (though not all finger prints! -though the chance does exist). again the possibilities are still there, so should peole die when there may be some doubt?
Lastly, since you are not on the jury, (and thank god for that since you've already made up your mind) who are you to say whether Micheal Jackson is innocent or guilty? -I don't want to turn this into a dispute about a legal case.
But there is evidence both for an against, a lot of the evidence against him has been discredited and the testemonies of people have been cast into disrepute. The kid who started it all stood in court and said he'd never tried to sell his story...
until tapes were played of him contacting Jay leno trying to sell his story.
I'm sure you won't see the point I'm trying to make. So I'll try to make it a little clearer.
The death penalty is only used in very high profile cases, and that is quite possibly the problem, in a high profile case, a lot of the time, there are people with twisted ambitions, people who feel they can get something out of it, or sell their story, and this quite a lot of the time, (as in the previous example) distorts what people say, they stand up in court, swear to tell the truth and then lie for their own gains.
If the death penalty were allowed it could be a case of some poor person (who is innocent) dies so that someone else can make a few thousand pounds/dollars selling their story.
Do you really think that is right?