AXE-wielding robbers threatened a security guard in Oldbury yesterday and escaped with a cash box.
But the gang of four were spotted by an eagle-eyed member of the public and arrested by police a short time later.
The security guard was forced to hand over the cash box by two men armed with axes as he left Tesco Express, Bristnall Hall Road, shortly before 2pm.
They ran off along Beeches Road before getting into a car and were then spotted in Arden Road trying to smash the cash box open.
A police spokesman said four men, aged between 21 and 36, were arrested on suspicion of robbery and remain in custody this morning.
Anyone with information about the robbery is asked to contact Force CID on 101 or anonymously to Crimestoppers on 0800 555 111.