Makes me feel a little like Daffy, when Bugs has just tricked him into saying "I am a rabbit" during rabbit season.

From your link:
"Whatever harm is done in the beginning to this person could very well defeat our purposes" My dad (crazy paranoid leftist) used to use threats to call the police or sue as his opening bargaining statement. Since the time I was an adolescent (and very prone to argue with him), I tried (unsuccessfully) to convince him that you can't back down from a position like that once you take it. But if you start with something more gentle, you can always escalate later.

Once you prove you are an enemy, you can't play any friend cards. Once you show contempt for a fundamentalist's religion, he will associate you with Satan. That can only drastically reduce your chances of success.

Apologizing in advance for the unrelated "red meat" included in the following link (and realizing that we will probably be sidetracked by the "red meat" anyway):

FBI agents told Pentagon officials that the military's harsh interrogation tactics in Cuba would produce "unreliable results,"

and FBI officials said in the documents that agents preferred the bureau's long-accepted, court-approved interrogation policy of building rapport with detainees to obtain information about terrorism.

and The FBI official also recalled a conference call with unidentified Pentagon officials in which he criticized the quality of intelligence gleaned from one detainee.

Here is a bigger treatment of the subject of interrogations. Note that this treatment assumes a limited amount of interrogation time. Also it assumes that the purpose of the interrogation is to get information that is very detrimental to the subject (self-incrimination). That should be somewhat more difficult than getting info that may or may not incriminate other parties.