I'm sure they're looking at who this cop testified against, and compare it to who if any have been released. There are vengeance killings that all cops have to be careful of. Judges as well. The smart criminals won't talk about it in prison, or anywhere else. They'll just gather what information they need and act. Cops, judges, and witnesses are not difficult to look up, especially in today's world of mass information technology. Addresses, phone numbers, car registrations, etc., are easily found on difficult to trace computers available in public library's and other places. I have a feeling this wasn't random. Someone had it in for this guy, and obviously planned it very carefully.