HELP ....is this this show?....(spoiler maybe)

Ok so I only saw half an episode awhile back but here is what i remember.....lol bare with me here

It was about this detective who was interviewing killers. Each killer said they met some guy at the same park and he wrote a name in the sand box or something.
There was also this older cop who said the killings tied into an older unsolved case or something about missing kids...so ya thats about all i remember

ALSO - i dont remember a Dr. being in it, just cops so maybe its not this... i dont know

so what do you guys think? thanks for any help