Police would have had a number of competing theories at the beginning of the investigation into William's disappearance, hence the extensive misper search of the area surrounding his foster grandmother's residence initially. As we have witnessed in MSM, the focus of their investigation has evolved over time.
Regardless, I think police would have a fairly good idea of the circumstances of William's disappearance and a strong suspect or suspects. Also, it now seems their focus is on covert surveillance of said suspect or suspects until they can recover William and make an arrest or arrests in relation to his disappearance.
BBM, Where is this info. or is it your opinion? Haven't seen anything in msm so just asking.