The 3 teenage boys had been hanging out one night. One boy left to walk home and was never seen again. His two friends were interviewed but cleared.

Years later a new investigator was assigned to the case. He looked over the interviews with the two friends and realized that when one of them was talking about what they did after the victim had gone home, he said something like "and then we all walked over here." The investigator thought it was weird that he'd said "we all," as if there were more than two people there. As if the victim hadn't actually left to walk home that night.

And that was what brought suspicion on them and they ended up being charged with the murder. They lead investigators to the remains that were under some tree roots in a local forested area. It was an area that search crews had originally combed, but had happened to miss the body.

It took place in the US. I think it was in the '90s but i could be wrong.

I saw this about a decade ago on an episode of (I think) an ID show. The victim's sister was interviewed for the show.