Witnesses reported at least three Blackhawk helicopters flying in close formation, then separately, around offices and residential buildings for several hours.
Several smaller A/MH-6 Little Bird helicopters were also seen circling close to the Chicago River. The choppers are often used by military special forces.
Witnesses described seeing three or four military personnel hanging out of each of the helicopters brandishing automatic weapons.
The following stunning videos show just how close the choppers came to the buildings, literally rattling windows as they flew past: