i arrested the cardinal but he won't confess what must i do?

Hi Mephistophel24,

you should give us a bit more information in each of your posts, so that we clearly understand in which part of the game you are. What you have done before, which quest you are intending to solve and so on ... .

Given your last post about lotti frankmüller i assume your in act 1. And with cardinal you mean judge vallarian.

After you fought him at Dragon Rock bring him to the prison. You can ask the Sheriff there that you want to interrogate him. Vallarian wont say much, so after the short interrogation just go the intermediate judge "Jeremiah" which should offer to do court proceedings for Vallarian.