The courts in many countries, including UK and USA, are based on the adversarial system, where each side deploys its evidence to best advantage while a neutral judge and jury weight up the evidence presented to reach a decision (the judge rules on whether any particular item of evidence is legally acceptable). Neither judge nor jury has any power to ask questions or carry out any kind of investigation themselves, but must rely entirely on the evidence presented by the opposing sides.
In other countries, such as France, the inquisitorial system is used, under which the judge carries out his own investigation with the object of determining what is the truth of the matter.
Both systems are open to prejudice by judge and, when used, jury. Research carried out quite a long time ago (sorry, I cannot at the moment remember the details – I think it was in a book I read long ago and still have somewhere so I’ll look it up) shows quite clearly that the belief by many people that they can tell when people are lying is simply a delusion. The supposed symptoms of lying are much more commonly the result of shyness, embarrassment or simply pressure from a persistent hostile barrister, trying to exploit just such a weakness to create a false impression of dishonesty on the part of the witness. Prejudice also often arises from a person’s appearance, either their dress or all too often simply their features.
It seems to me obvious that the purpose of the court should be to uncover the truth so as to deliver real justice, but a judge carrying out his own investigations prior to the trial brings with it a much enhanced probability of prejudice. I therefore think a sort of hybrid of the two systems should be used.
The judge and, especially, the jury should have the right to ask their own questions and even to call additional witnesses (but with the judge continuing to rule on the acceptability of the questions), so that the purpose of revealing the truth supersedes the simple contest between two lawyers. To prevent prejudice completely, all evidence should be in writing (probably on computer screens), with neither the judge nor the jury seeing any witness, plaintiff, defendant or lawyer until after the verdict has been declared. The trial would therefore in many ways resemble an on-line chat system.