I've NC for this - not too sure why really.
I used to work for a council boarding up empty properties. Our instructions were to shout through the door something along the lines of "Is anyone in there? Please make yourself known, we're about to board up the property" when we first arrived and then again just as we were about to start.
We were told not to enter the property because we wouldn't be insured to do so if we had an accident. The inside work (deep cleans, clear outs etc.) were done by another team.
Several times we encountered squatters who usually came on the second call, or a few times when they heard the drills starting up.
What I'm trying to say is that I can see how his body might've been boarded up inside given council bureaucracy and a totally reasonable "not my job, guv" attitudes among council workers.
I'm in England and this was several years ago. Might be different in this context of course.