Re: Separation of powers
DS999,
Thanks for reminding me about the grand juries. One of those things where they've disappeared in the UK, so it's easy to forget that the US and our systems have diverged significantly over the years, from being very similar - but with King crossed out and President quickly written in. Of course, having a constitution always made the US system completely different anyway, but also means it's evolved less - because it's much harder to change a codified constitution than a system of written precedent and proceedural law.
We got rid of those (it turns out when I Google it not in the 18th Century, but) in 1933. Although they'd apparently been increasingly irrelevant in the 19th Century due to the system of a hearing before a magistrate to see whether a suspect could be held in custody by the police prior to charging. After that prosecutions were brought by the Attorney General (a government minister but by precedent they were supposed to act impartially - which they mostly did). In practise the police tended to make those decisions in cooperation with prosecuting barristers/lawyers. That allowed the police too much leeway to basically let crims off prosecution in exchange for deals - and allowed some dodgy prosecutions - so we created an independent Crown Prosecution Service (CPS) who mean the police are no longer allowed to stop investigating someone without CPS permission, and also can't charge without it either. Although I think the Attorney General can still bring prosecutions, in exceptional circumstances or matters of National Security.
However, Grand Juries aren't particularly hard to cheat at, so I think your hope in them is misplaced. Seeing as they don't sit in public and the government controls all the evidence they see - it probably isn't hard to get them to allow charges to be pressed. Even if the evidence is so flimsy that the subsequent court case collapses embarrassingly quickly.