Personally, I have been trained in both the REID Method and Glen Foster's Kinesic Interview & Interrogation techniques. Interesting what he says about "Enhanced Interrogations".
But he does score some points w/ me regarding various law enforcement techniques that are very effective, such as the methods I mentioned above that are not seemingly used.
Interviewing to me, is the fact gathering- fishing for info from the person that you target.
Ask multiple questions-don't challenge the answers-let them talk, see if they answer the same, and/or elaborate more in their answer.
If you have 2 suspects or more interview separately-and keep them separated from time they are taken custody- big error allowing them to ride in the same transport vehicle, need to cross check all questions & answers with both. See what are similar/different.
The Interrogation period is where you have all your data in hand; including any intelligence from team members, statements, witnesses. etc. and point blankly tell the person and challenge their answers b/c you have info supporting that challenge-
sometimes I disclosed some info., if minor but would hold it over their head as a stressor to keep them on edge.
If they answer questions with ''Honest to God", "On my Mother's Grave" and any such comments clarifying what they said with the mention of the Deity or their Children's Lives are red flags to the fact that they are lying/and or guilty at what they are accused.
A person that is not guilty of a crime, etc. will have constant answers nor the need to swear or attest his answers upon his family, children or God.
Just some interesting facts of the JP method of I & I.