From ABC7 in Chicago:
March 16, 2006 - Chicago police are investigating cases of suspicious activity at two Loop buildings. One of them is the Sears Tower.
Since 9-11, the Sears Tower in particular has turned up on several lists of possible targets for terrorists. ABC7 news has reported sightings of suspicious looking individuals photographing the building numerous times in the past several years. Law enforcement officials have always publicly downplayed these incidents and they attempted to do that again Thursday.
I think they call these hideously deformed creatures "tourists." Cops should be allowed to shoot on sight, I say.