Would this situation lead you to do an interrogation or an interview?
You are a probation officer who was conducting a home visit for probationer Bobby Jean. You walk up to the door, she answers, and you notice a bag of marijuana sitting on the kitchen table. She promises that it is not hers. You provide her with a urine screen and it is clean.
I would argue that this situation warrants an interview, but not a full interrogation. The most important factor is the fact that the probation officer did a urine screening on the probationer and the urine screen showed no evidence of drug use. Given this situation, her story seems very plausible. The best course of action would be to conduct an interview in which the officer finds out what people have access to her house and might do things like bringing illegal drugs. The officer should counsel Bobby Jean about the legal danger to her of having these people around. This would be more useful than a full interrogation about whether she has violated her probation.