Ronnie Biggs was perhaps the most well-known member of the gang, primarily for his escape from prison and for his life abroad during which he taunted the detectives who sought his recapture. Biggs and a dozen of the gang were caught, tried, convicted, to sentences ranging from three years to 30. A handful of the gang, however, were never caught and some were never identified.

One of those mystery men was referred to repeatedly the rest of the gang only as "the Ulsterman." This man was thought to have been an insider who provided to the gang crucial information about Royal Mail train routes and routines; further, he was assumed to have absconded with his share of the stolen money.

Five years ago, a television documentary, based on interviews with gang member Gordon Goody, identified "the Ulsterman" as Patrick McKenna, a former postal worker from Salford who had died in 1992. McKenna's family couldn't understand why Goody had named McKenna, who had worked for the postal service but knew nothing about the railroad, lived in a modest house all of his life, and left his family just £ when he died.

Based on fresh evidence compiled by retired transport detective Graham Satchwell, who has made the Great Train Robbery a focus of his studies for many years, authorities now believe that "the Ulsterman" was Sam Osterman, a known underworld figure who counted among his friends Tommy Wisbey (left) , one of the men who robbed the train. Satchwell interviewed Wisbey several times, and Wisbey identified Osterman as "the Ulsterman." A book laying out other proof gathered by Satchwell will be out soon.