The masked suspect was possibly armed when he entered the CVS store at 5100 Broadway. Employees were evacuated and police had surrounded the building by 8 a.m.
Police believed the suspect might have still been in the building and a perimeter was established in the neighborhood.
A SWAT team responded and issued orders to the suspect before entering and clearing the building. The suspect was not found inside, police said.
Police said that surveillance video showed the masked man walking up to a counter in the store, then exiting the rear doors of the building before police arrived.
Normal business at the CVS was expected to resume shortly. The large store was scheduled to open at 7 a.m. today.