I was watching a cleanup crew coming out of an airplane while i was waiting for my own plane, and i wondered the same thing, Why isn't there someone supervising these people?
It is sort of like the Russian school incident. That was carried out due to the people who worked for the school over the summer. They were the ones who planted the bombs for the terrorists, weren't they? So definately the clean up crews, etc. should be made to go through an exstensive background check.