What's in the Box?
The cardboard box in the basement of the police station is like a smaller, sadder version of the woods. Rob's crime occurred about twenty years ago and, frankly, no one cares except for Rob. When he goes down to dig through the files, he says, "I doubt anyone had touched it since" (4.74). It may be sad for Rob, but it's also totally true: No one cares about the case anymore.
Just like with Rob's memories, the case gets smaller and smaller the older it is. It gets packed up, put away, and forgotten. The lives of the missing kids, Peter and Jamie, have been condensed down to one small, neglected container.
If Rob hadn't been involved in the Devlin case, no one would have made the connections between the current case and the old one… and that might have been for the best. It's not like they uncovered anything about the old case while investigating the new one, and instead all that happens is Rob's old wounds are re-opened. The box, then, symbolizes the past, its diminishing relevance, and Rob's inability to completely let it go.