WOODLAND HILLS (CBSLA.com) — Police looked for a possible gunman inside two buildings in Woodland Hills Monday afternoon.

Los Angeles Police Department officers responded to reports of an armed man on the 10^th floor of one of the structures at Farmers Plaza in the 6300 block of Owensmouth Avenue around 3:30 p.m.

Authorities immediately surrounded and evacuated the plaza’s two 11-story buildings.

KCAL9′s Joy Benedict reported that no shooter was found after a comprehensive search.

Benedict said detectives told her that the person who initially contacted police about a potential gunman allegedly found a threatening letter, which may have been mailed a week ago.

The investigation is ongoing.