However , based on scrutiny with modern telescopic lenses , it has been claimed the buildings are mere concrete shells lacking window glass or even interior rooms , with the building lights turned on and off at set times and the empty sidewalks swept by a skeleton crew of caretakers in an effort to preserve the illusion of activity .
However scrutiny with modern telescopic lenses reveals that the buildings are mere concrete shells lacking window glass or even interior rooms , with the building lights turned on and off at set times and the empty sidewalks swept by a skeleton crew of caretakers in an effort to preserve the illusion of activity .