How it's done...

WASHINGTON -- It took hours for officials at a downtown Washington bank to realize they'd been robbed.
Police said a man impersonating an armored car guard walked out of a Wachovia bank branch on Pennsylvania Avenue Thursday after officials let him sign for a locked bag of cash. About $350,000 was taken, law enforcement sources told News4.

About an hour after the robbery, a real Brinks guard arrived at the bank and was told that another guard had completed the day's cash pickup.
Police said the Brinks driver waited until he returned to his office to tell his supervisors about the failed pickup. Brinks officials contacted the bank, and a branch manager called D.C. police about 8 p.m. -- almost 11 hours after the theft.
"Around 9:30 in the morning, we had a gentleman entered the bank who was dressed in ... maybe a Brinks-type uniform walked in and signed for the money and walked out," said D.C. police Lt. William Farr.
The bank is across the street from the J. Edgar Hoover FBI building. The FBI is investigating.
Authorities don't have a detailed description of the robber and don't know whether he left the bank in a vehicle or on foot.
A similar robbery took place at a BB&T bank in Wheaton, Md., on Wednesday. A man in a uniform resembling an armored guard service uniform went into the bank and presented himself as a substitute courier, saying the regular courier was on leave, according to Montgomery County police. The man picked up an undisclosed amount of deposits and left.
On Thursday, according to police, the regular courier went to the bank. It was then determined that the man who picked up deposits on Wednesday was not authorized to do so.
Authorities are trying to determine if the incidents are related.