In a release timed at 3.41am, Herts Police confirmed that 55-year-old Ian John McLoughlin had been taken into custody at an address in London.
He was arrested at about 1am and is now being held at a police station in Hertfordshire and questioned on suspicion of murder and robbery.
Detectives involved in the search for McLoughlin have thanked the public for the support they received after appeals for information.