DENVER -- Denver police are investigating the armed robbery of a southwest Denver grocery store just after midnight.

According police, three employees were duct-taped during the apparent robbery.

Officers got the "robbery in progress" call at 12:46 a.m. from inside the Grocery Warehouse at South Federal Boulevard and West Louisiana Avenue.

Police thought the gunmen were still inside when they arrived and called in the SWAT team and a negotiator to talk them out.

The store employees came out of the store at about 2 a.m. and police discovered the robbers had already left. Investigators believe the two men escaped between the time the employees were tied up and the employees were able to call for help.

Police aren't sure what the two gunmen wanted, since the store was closed and the store's money was not available. They have sketchy descriptions on the two: one possibly had an East Indian accent and the other had a Hispanic accdent.

Investigators aren't sure if the robbers fled on foot or in a vehicle.