Again, don't feel like retyping again and again. I just think it likely that investigators - and dogs - missed Brian's body. All things considered, accidental death in the building, remains still there, seems like most plausible scenario given all the facts. One person of hundreds in the building that evening went permanently missing. One person of hundreds caught on vid entering the building that evening did not appear on vid leaving. Are these two oddities linked by causality? I think most likely so.
There are no facts leading toward Brian being buried in the construction area.