When Ahmed looks at the floor there are two rifles placed next to each other, as he takes one step forward both guns are between his feet.
The hostage crisis takes place on the 7th floor but the number eight appears on the wall by the stairs.
The police already had a (mistaken) description of the terrorists through the child who delivered the radio, and would have arrested Rashad upon exiting the building due to him being the only one matching the description. Also, many people (including some security guards) saw Ahmed (the real terrorist) and fled before the standoff began, and thus the police would have had a description of him too.