That's the whole point of the system. Prosecutors are supposed to prosecute those they believe are guilty (of course that doesn't mean negligently or willfully

That's the whole point of the system. Prosecutors are supposed to prosecute those they believe are guilty (of course that doesn't mean negligently or willfully ignoring evidence that points toward innocence). While the system is supposed to presume innocence until proven guilty, it's the job of the prosecutor to prove guilt.