What can I legally do to criminals?
I found it on the wiki. It was under the page for your Court.
Crimes are actions that allow a character to imprison someone from their realm without incurring tyranny and may be personal, familial or religious. Some crimes allow additional punishments such as Title Revocation, Banishment, or Execution.
Personal crimes are caused by certain actions taken against a ruler and allow that ruler to imprison the criminal character.
- Attempted Abduction - Abduction scheme fails on the character.
- Attempted Arrest - Liege requests imprisonment and character refuses.
- Attempted Elopment - Elope scheme fails on the character's spouse.
- Attempted To Murder Me - Murder scheme fails on the character. Banish, Execute
- Blinded Me - Blinded the character.
- Botched My Treatment - Court physician's risky treatment of liege failed. Banish, Execute
- Castrated Me - Castrated the character.
- Declared War - Declaring war upon the character. Revoke Title
- Elopment - An elope scheme succeeds on the character's spouse.
- Failed To Treat Me - Court physician's safe treatment of liege failed.
- Revolted against Me - Civil war ended in white peace. Revoke Title
- Refused Imprisonment - Vassal refuses imprisonment and realm has High Crown Authority. Revoke Title
- Refused Retraction - Vassal refuses vassal retraction and realm has High Crown Authority. Revoke Title
- Refused Revocation - Vassal refuses Title Revocation and realm has High Crown Authority. Revoke Title
- Scheming Against Me - Discovered as agent in a scheme against the character.
- Spying on Liege - Spymaster fails the Find Secrets task on the liege.
- Tortured Me - Tortured the character.
Familial crimes are caused by certain actions taken against a character and allows any ruler from the same family to imprison the criminal character.
- Attempted To Murder Family Member - Murder scheme fails on a member of the character's family. Banish, Execute
- Botched Treatment of Kin - Court physician's risky treatment of liege's family member failed. Banish, Execute
- Failed To Treat Kin - Court physician's safe treatment of liege's family member failed.
- Murdered Family Member - Murder scheme fails secrecy on a member of the character's family. Banish, Execute
- Tortured Family Member - Tortured a family member of the character.
- Unlawfully Executed Family - Executed a family member of the character without a valid reason. Banish, Execute
Religious crimes are caused by traits that are considered criminal by a faith and allows any ruler to imprison the criminal character.
- Excommunicated - Character has the Excommunicated trait and faith has the Communion tenet. Revoke Title, Banish, Execute
- Known Adulterer - Character has the Adulterer trait and faith has the criminal adultery doctrine for their gender. Revoke Title
- Known Cannibal - Character has the Cannibal trait and faith does not have the Core tenet Ritual Cannibalism tenet. Execute
- Known Deviant - Character has the Deviant trait and faith has the criminal Doctrine deviancy doctrine. Revoke Title
- Known Fornicator - Character has the Fornicator trait and faith has the criminal adultery doctrine for their gender. Revoke Title
- Known Sodomite - Character has the Sodomite trait and faith has the criminal same-sex relations doctrine. Revoke Title
- Known Witch - Character has the Witch trait and faith has the criminal witchcraft doctrine. Execute
- Known Kinslayer - Character has a Kinslayer trait and faith has the criminal kinslaying doctrine for its severity. Revoke Title
There appears to be a (very small) fourth category, Dynastic crimes, which I assume allow a ruler to imprison a criminal character from their dynasty?
- Denounced - Character has the Denounced trait.
https://ck3.paradoxwikis.com/Court#Crime
The key is that "Known Criminals" have a little ball & chain icon on their portrait. When hovered over, it expands:
Further research has revealed that these modifiers are defined in the game's opinion_modifier files ( steamapps/common/Crusader Kings III/game/common/opinion_modifiers ) which the Wiki has already compiled into a nice table, available here: https://ck3.paradoxwikis.com/Court#Crime