I agree that it is curious that LE has had so much contact with this guy. To tell him that we're going to be talking to him again, and tell him when, definitely seems like they are turning the screws. This type of thing would rattle most people, especially people who have potentially been involved in a (serious) crime. Perhaps they are hoping that if he is in fact involved, he will respond with an overt act that will aid in the investigation (dump evidence, return to crime scene, etc.). If this is the case, then he is almost certainly being surveilled.