Okay, I have to make a few assumptions to come at this.

First, that because you’re using English, you’re going to be most interested in an answer framed about the systems of the countries where English is a, or the, main language used.

Second, that you don’t want a shit ton of detail, because you otherwise would have looked possibilities up yourself, because there’s character limits.

Third, that because you asked here, that you don’t want a pile of links (which I’m rarely willing to do nowadays anyway).

So, here’s my general purpose answer within those assumptions, which means precision and accuracy aren’t 100% a factor. None of this applies everywhere.

So, we gotta start with trials. A trial assumes a state, as in a government of some kind. Could be as small scale as a clan or tribal council, could be as big as a nation.

If you don’t start there, it gets crazy trying to fill in.

A trial, by definition, is when the body of the populace (the state), regardless of the organization of that populace, accuses someone of having violated the rules of that body. It’s the “state” saying : you did this, and the individual or group saying “nuh-uh”.

That’s the gist of what criminal justice is.

By the nature of such a thing, you have to have a way of deciding what is and isn’t okay during the trial, and you have to decide who determines the outcome. In monarchies, or feudal systems, it would be whatever ruler is in charge, though they may delegate that decision (as in a crown prosecutor, and judges)

Point being that a trial is inherently adversarial. It’s an accusation against a person or persons, and them having to refute that.

In order to bypass that, you have to eschew any organization of people at all. It’s person vs person, no trials, they hash their shit out. Which is still adversarial, but we have to limit this.

So, there’s always sides when there’s a disagreement. It’s unavoidable. If the state says you did it, and you say you didn’t, and you’re allowed a defense at all, the only question is what sides do what, with what resources. A panel of judges is just as adversarial in practice.

When did that start? At least as far back as written history. It’s a dilemma that’s human. You ever have a sibling or other relative say you did something? If you didn’t do it, or you don’t want to admit you did, until that issue is resolved, shit is unpleasant.

If it’s your siblings, mom and/or dad make the decision, fairly or unfairly.

In a bigger group, it might be the elders, or whatever. Accusations of wrongdoing require resolution for a harmonious group.

When decisions are made by a single individual, like a king, you have to rely on that king being smart, fair, and even handed, as well as wise in handing out resolutions.

So, people all around the world have rules for that.

A lot of the kind of rules you’ll find in the US, Canada, Australia, and places that used to be owned by the British Crown, follow rules that originated as British law. Not every detail, see the initial assumptions and disclaimers already made. But, as a broad thing, the body of law built up in England heavily influenced law in places they owned or dominated.

A lot of that has origins in Rome and Greece, and other preceding cultures, but that’s outside the scope of this.

So, chances are that whatever legal system you’re asking about, came about because of the way the British Empire did things. But you can look to the Magna Carta for the more recognizable facets of it. That was a document setting out rules between the ruling people on how they would treat each other.

But the key to it is that people, in general, need protections from people in power. So those in power sometimes agree to have a system in place to minimize unfairness, at least on the surface (and that’s ignoring how successful that is or isn’t).

That’s how it came about, an attempt to spread out or blunt the power of the state against individuals.

Like you said, panels can work, as long as all the power isn’t vested in that panel. If your group of judges isn’t perfect, then it’s no better than a king making the decision arbitrarily.

In theory, having the state have to present a case, while the accused offers a defense, and a jury making the decision while a judge makes sure everyone follows the rules, should be the way least prone to corruption and even when it fails, it should still be a mitigation of abuses of power. Obviously, it doesn’t work perfectly. As long as the rules are applied evenly to all, and the base assumption is that the state has the onus of proof, that’s as good as it gets in terms of humans trying to make decisions about other humans.

To bring this to a close, let me apologize for things being disjointed. We have a rogue rooster to deal with, so I’ve been writing this in between handling stuff, which means my thoughts were not allowed to flow the way I’d prefer. So I know I missed stuff, and that it doesn’t all connect the way I’d prefer. But I gotta figure out what the hell to do with this little guy, and that means no editing.