1: somebody who maintains their personal integrity under pressure from legal authority
2: somebody who doesn't snitch
3: Alternatively, somebody targeted by the police or legal authorities because they believe he has information that he doesn't really have, and instead of making up information to tell to the cops and get off, takes the consequences like a man
Ex 2: He's a DeMuth; you would squeeze blood out of a turnip before you can get him to snitch.
Ex 3: "Did you hear they charged Jamie with conspiracy?"
"Yeah, they are trying to force him to give up names and make up information."
"That won't happen. He's no curtis jackson; he's a DeMuth."