The suspects disappeared into the building after depositing the weapons on top of a stairway vestibule on the roof.
Police officers emerged from another stairway vestibule approximately 10 minutes after the suspects went inside.
An officer climbed onto the vestibule and retrieved two to three weapons.
Officers discovered the weapons were air guns loaded with plastic pellets.
The fake guns are reportedly Airsoft-brand rifles, replicas designed to look like real guns.
Police determined there was no crime committed and were preparing to leave the scene.
The four individuals were detained but then released as it was determined no crime was committed.
Police had evacuated the area and established a perimeter around the building.
The building is located at 725 S. Main near 8th Street.
An LAPD air unit also responded.