At 2:49 p.m. on Monday a man walked into the Bank of America at 600 North Washington St., implied he had a weapon and demanded money, Alexandria police said.
The teller he approached handed over cash and the suspect fled, but not before a surveillance camera captured an image of the man witnesses described as at least six feet tall.
Police did not release the amount of money allegedly stolen.
The suspect, a black male, wore a dark-colored hooded sweatshirt, a light-colored coat, dark pants and a knit cap, police said.
The bank robbery was Alexandrias fourth this year, according to police spokesman Jody Donaldson. There were seven last year, he said.
As police search for the suspect, they encourage the public to call the Criminal Investigations Section of the Alexandria Police Department at 703-838-4444. Witnesses can remain anonymous.