This guard was taken hostage and recognized one of the workers from the club.  The man was not wearing a mask, and he was sleeping in a theater seat in the immediate vicinity of the guard.

…Many leading representatives of commercial and government agencies, including members of the Russian parliament, the firm Arkhont & Company were members and visitors at the gay club.  They are protected from examination by the law enforcement agencies.  It is possible that the club kept a database of its clients in order to collect compromising information on certain important persons for the purposes of blackmail.  This gay club (at the Dubrovka theatrical complex) was in an ideal location for the preparation and carrying out of the act of terror…