Britain's Scotland Yard revealed on Thursday that Flying Squad officers were ready to pounce when the unsuspecting robber walked back in to the bank branch at 5 p.m. that same day.
He had entered the High Street branch in Beckenham, Kent, just after 10 a.m. on Wednesday, January 31. He pushed a note under the counter, which carried a demand for a large amount of money.
He threatened to hack into the bank's computer system unless his wishes were complied with — and then arranged to return for the cash.
Not surprisingly, police were waiting for him when he turned up again in the evening.
Detective Superintendent John Shatford said, "This operation should serve as a warning to anyone thinking of committing a robbery in this way.
"The Flying Squad are extremely skilled in dealing with this type of incident and can respond quickly, as this operation shows."
A 33-year-old man was taken in custody on suspicion of blackmail.