I just don't think the COs probably interacted that much with the ISP, Sheriff's office or city police. They are their own branch. My last job was with the Sheriff's office and a specific branch within it. I rarely dealt with anyone on the Sheriff's office side of things, and then only if I needed a translator. I knew exactly 2 sheriff's deputies by name despite us all being in the same building and on the same floor. I dealt with zero city police, my only dealings with the highway patrol was via email requesting records for DUIs. I had no dealings at all with any DNR, CO, FSR officers at all.
I think just because it was a small town there is the assumption that all the branches worked together and were all in each other's business. But my experience with government, county, and state agencies is they do not work well together and do not communicate well together. I don't even think it's a matter of egos, it's more of they each have policies they follow and they do not align with other agencies.
So unless DD was friends with an investigator that was actively working the case, I can't see him just going in and saying hey I interviewed this guy, whatever happened with it, if he even remembered interviewing RA.
JMO