I was thinking about a few past cases that were recently solved, and it seems in many of them, there was always a third party that the murderer told/bragged to about the crimes, but then threatened to kill them if they spoke. It really makes me wonder about how many cases out there, there are people who do know the perp or the truth, but are afraid to come forward. I do think it's hard for any murderer to keep this info to themselves, and that they would want to tell someone, whether bragging or clearing their conscience, etc...

I think most of the time police know or have a strong feeling of the perpetrator but just don’t have enough evidence to charge him/her.