What an interesting read, thank you for the link!

I'd encourage everyone to read more about his life before and after becoming an interrogator, but I found a tl:dr of his methods

The Scharff Technique was defined by four key components: 1) a friendly approach, 2) not pressing for information, 3) the illusion of knowing it all, and 4) the confirmation/disconfirmation tactic. (The latter strategy is when an interrogator presents a claim in the hope that the prisoner will confirm or disconfirm it—it’s what Scharff used to learn about the tracer bullets.)