Historically, what they do is to prove guilt. They go through all kinds of testimony and documents and investigation...and then they get to the point where guilt is proven.
They get to the point where they have incontrovertible, undeniable, absolute proof that a crime was committed. And that is the point that it always ends. They are good at proving crime and guilt. They do that all the time. But then, nothing happens.
Investigating is not the problem. Congress investigates all the time. The problem is there is never any prosecution.
To put this on the ground level, it would be as if I robbed a bank, and they knew I robbed the bank. They call me in to testify and I declare that yes, I robbed the bank. And then they all slap each other on the back and high five and congratulate each other. So I say, What now?
Nothing. You can go. We solved the investigation. That's all we care about. Bye bye....off you go...