How desperate are you?
Your emotions and demeanour play a huge role in the likelihood of your subject cooperating and providing the truth. Imagine the effect of you, the interviewer, becoming agitated or aggravated during an interview. If the interviewer becomes agitated, it clearly demonstrates to the subject that you are desperate for the confession; and as a result, this can make the confession more difficult to obtain.
Think of the basic principles of supply and demand. Just like if you go to buy an item and you appear desperate to make the purchase “it’s exactly what I was looking for” the salesperson has no need to lower the price.
However, if you don’t appear desperate “I want to check your competitors and see what they offer” they may be willing to move on the price. Reverse the roles and think about the overzealous salesperson. When they are desperate for a sale, you become suspicious of their neediness. The same holds true for your demeanour as an interviewer.
When interviewers conduct a thorough investigation upfront, they are able to enter the interview with credibility rather than relying on a confession to complete their investigation.
This will change your leverage during the conversation. In these cases, it should become clear to the subject that the interviewer does not desperately need the confession, which should make the confession easier to obtain.