Medical Detectives/Forensic Files is awesome, used to watch it before falling asleep lol. I think the production was pretty spooky and all the shit being real life made it all the more creepy.
I remember an episode called X Marks the Spot - a short explanation, it's about some dude killing prostitutes, he actually took them home and torturing them in his basement, they actually find some video tapes in his home (some mild portions you can find on the internet and on some other documentaries). They found him through some specific map that he downloaded from the internet which he printed and sent to fuck with the investigation. Turned out it was downloaded just from his IP address. Fascinating stuff.
There are many other great episodes as well, but this one came to my mind.