ROYAL OAK, Mich. -

Investigators in Oakland County believe one man has been pulling armed robberies one after another.

Since December, the man has struck in Madison Heights, Berkley, Birmingham and Royal Oak. Another robbery happened Friday in Royal Oak.

He brandished a handgun Friday morning inside a Citizens Bank. According to a police source, he ordered employees and customers onto the floor. He escaped with an undisclosed amount of money.

The same man is expected of a crime spree which began with an armed robbery at a 7-Eleven, but he prefers banks. He has hit six of them.

He is described as African American with a medium build and standing between 5 feet 8 and 5 feet 9 inches tall. He has been seen wearing a black winter cap with a brim. He has placed money in a black, laptop-style bag.