This is the saddest thing ... (from your link). Potentially allowing so much time for the perpetrator to cover his tracks. And/or for nature to conceal/destroy forensics. And/or for William to be relocated and hidden more thoroughly.
.... the investigation, while high-profile, was also chronically under-resourced and “often thousands of pieces of information behind” with “thousands of investigative notes” and possible tips and sightings not followed up, as well as “days and days and weeks’ worth of surveillance device material” not listened to.
I wonder if they have listened to all of the surveillance device material by now? So many clues that perhaps are still sitting in William's file.