I have jury duty next week. This has led to me spending time thinking about the model of justice we use. Let's suppose you want to figure out the true circumstances of, say, a robbery. The police have a suspect and evidence. The case comes to trial. This is the big moment where guilt or innocence will be judged -- likely a life-changing decision for the accused. To make this life-changing decision, you bring in 12 individuals from the general population with no particular experience of law or robbery. You disallow them access to any external resources they could use to educate themselves. You forbid them from considering anything not mentioned during the trial. You pass them through a screening process which serves in principle to ensure impartiality, but in practice to eliminate individuals the attorneys think they won't be able to sway, that is, those intelligent enough to see through rhetorical tricks and those more likely to make decisions based on fact and logic rather than emotion. Then you start the trial.
On one side, you have the prosecution team, representing the office of an elected official with a vested interest in looking tough on crime and successful in putting offenders away. On the other side is a defence team, paid to ensure the best outcome for their client, regardless of justice. In the middle is a judge, often also elected and tied in to party politics and thus with a vested interest in taking a certain stance towards crime. Although the jury is charged with determining guilt or innocence, they have no opportunity to ask questions of witnesses, no opportunity to witness the scene of the crime, and no opportunity to examine evidence or background information that might well be relevant but which is considered "inadmissible" based on an arcane set of rules interpreted by the judge. Every attempt is made to control the jury's view of the case.
When the arguments have been completed, the jury retires to consider a verdict, but not before receiving instructions from the judge, who thus has the opportunity to frame the case as he/she sees fit and may even direct a guilty or not guilty verdict. Once the jury does retire, it must decide the case based on one of three standards: "on the preponderance of the evidence"; "on clear and convincing evidence"; or "beyond all reasonable doubt." All of these standards are subjective, especially when the evidence itself is only available through the lenses of prosecuting and defence attorneys. Although in principle the jury is to weigh only the evidence presented in the courtroom, in fact each jury member will bring in their own pre-formed biases and judgements, as well as subjective impressions of the defendent and the attorneys. The very principle that jurors be "peers" of the defendent reduces their ability to dispassionately decide on the evidence.
The system is clearly not about justice or truth. The purpose of the lower courts is not, in any case, either of these. Rather, the court is there to apply the law, regardless of whether that law is just, or whether the determinations made through the court are true.
Jury systems differ significantly from country to country, with some countries not having such a system at all, and others limiting jury trials to only the most serious offences. The history of jury trials in English law goes back a long way. In the beginning (10th century), "jurors" were not picked from among the people. Instead, they were picked from among the minor nobles, who likely had some experience with settling disputes. They did not sit passively as facts were recited by attorneys. Rather, they were responsible for going out and determining what happened themselves, then reporting back. Then, as now, they were required to swear to investigate without bias, and indeed the purpose of the jury seems to have been to stop those in power from arbitrarily getting their own way. While the composition of the jury changed over time, the idea that jurors ought to investigate the case themselves persisted until the 17th century. Even if we decide jury trials are worthwhile, then, there is no reason that we must have the system we do now.
Historically, jury trials functioned in an environment without full-fledged police forces with trained detectives and forensic labs. Coming from this background, it makes sense that jury trials focused on witnesses. Witnesses, however, are unreliable even when not directly biased. Properly applied forensics does not have this problem. Forensic evidence does, however, need to be carefully considered both for what it does and does not show. Forensics-focused TV programs give a false impression -- their goal, after all, is an interesting plot, not accuracy. But where else in life does the average person encounter forensics? A jury taken from society in general is in no position to evaluate expert scientific testimony, especially when both sides can produce experts supporting their position. Judges are likely in no position to do this either.