Show an act of guilty or not guilty?

You can feel 'guilty about' doing something, but you are 'guilty of' a crime.

He realizes that everyone is dying that is close to him and they have shown that it was his fault for not listening.

Whichever court you are being tried in determines your sentence.

Yes, you can.

If you are guilty, you did the thing you are accused of doing. If you are not guilty, you did not do the thing you are accused of doing.