Well, as we saw last Thursday, the government prosecutor doesn't have absolute power.  I would say that the degree of corruption in the office of prosecutor varies considerably, from little to a great deal, though never, in my opinion, absolute. Of course there are prosecutors who hide evidence in various ways, and there are prosecutors who refuse a retrial based on exonerating evidence.

In this case, the jury not only questioned the prosecutor's case, it conspired to have a hold-out juror dismissed, so that it could reach an unanimous decision to acquit.