True. Though the investigators did not make that same assumption.
"Police searched each of the 21 houses in the estate that surrounds Benaroon Drive, the street just outside Kendall where William’s grandmother lives. They searched the houses not once, but three and four times, each time using different personnel to make sure a fresh set of eyes looked at every possible clue.
Roof spaces, sub-floor spaces, wall cavities, cupboards, sheds, all were searched and searched again with methodical determination just in case someone was keeping the little boy hidden. Even the grandmother’s house was searched, top to bottom, but there was nothing. Not a scrap of clothing, not a footprint in the dirt, not an errant tyre track.
Police dogs were brought in and they managed to find William’s scent, but only within the boundaries of the backyard."
https://www.nowtolove.com.au/news/latest-news/spiderman-found-in-search-for-william-6771
All the homes in the estate were searched. And then searched again. "We have had police through three times," Richard Wilson says. "Every cupboard, they have had a look in the ceilings, have had a look in the boots of cars."
http://www.smh.com.au/nsw/missing-william-tyrell-casts-dark-shadow-over-town-20141031-11fbdi.html