Part of the problem, for all of us, is we don't know exactly what "completely dug up" means in this particular case. And we don't know how much time elapsed before construction crews knew about a missing man, and what construction activity might have gone on before the search of the construction area took place. Or at least, I don't have that information.
The search of the construction area really means very little (at least to me) unless it was done very soon, like the very next day, after the night Brian went missing. I highly doubt the construction company held off work during those early days of Brian being missing--unless LE required them to stop, as usually there are financial penalties if a project is not completed in a certain timeframe, etc.
Also, I don't know if any footings, etc., were required for this construction project, necessitating deeper trenches than you might find for house footings, but "Trench Deaths: A Tale of Two Dakotas," a blog post at jordanbarab.com, illustrates why a trench collapse is so deadly.
If you are not familiar with commercial construction, then you may not know how extensive the ground work might have to be for a buildings built to a specific code.
Reading about people found dead who were caught between walls, in chimneys, locked stairwells, etc., gives rise to what's possible, even if it doesn't seem probable.
Brian went missing in a very short period of time, not seen on any surveillance video as leaving the building, with a "completely dug up" construction area right there, his phone went to voicemail immediately, and a horrible smell emanated from somewhere in the building around this same timeframe.
moo