Ignorant jurors: I understand that lawyers cannot serve on juries (in at least some states they may be jurors, but are often excluded); they would dominate juries, and besides, the jury should get explanations of the law from the judge, not from one of the jurors. Fine. But for a similar reason, potential jurors who have some expert knowledge that pertains to the case (medicine, science, DNA) will be excluded from the jury. They might tend to dominate the jury. But also, many lawyers do not want a jury that can understand the evidence in any way.

Technicalities: They throw out convictions, based on "technicalities." They didn't read you your rights. You got an unfair trial for one reason or another. Somebody made a mistake, and you get a new trial, or even go free. Should that be? In general, these technicalities are abuses of the defendant's rights. How do we prevent such abuses? We can't just warn judges, prosecutors, and the police. That won't stop the abuses. As far as I can see, the only way to prevent these abuses is to throw out convictions on "technicalities." What other way is there?

Presumption of innocence: You are presumed innocent until proven guilty. This means that the prosecution has to actually show evidence and prove you guilty, for you to be found guilty. Sometimes prosecutors don't seem to realize this, and don't bother to prove their cases. The defence doesn't actually have to prove its case, except to make the jury doubt the prosecution's evidence. Of course, this only applies to the jury; the police and the prosecution do not presume that you are innocent.

Expert Witnesses: Expert witnesses can state their opinions on the witness stand (other people cannot). And juries are often encouraged to believe them without real evidence. Some of these expert witnesses are not real experts. I think an expert witness should be a person who can explain something technical so the jury can understand it, not someone who is believed without explanation.

DNA fingerprinting: DNA evidence is perhaps the best thing to come along in the cause of justice (convicting guilty people and freeing innocent people) in the history of the world. It is more distinctive than fingerprints. It is much more reliable than photographs and video tapes. It is more reliable than a confession. It is much much more reliable than eyewitness evidence of any kind. And it is sometimes suppressed. It is not perfect. The tests can be botched. Test results can be switched. Expert witnesses can lie about all of this. The same is true of any kind of evidence, however.