An archive detailing the Great Train Robbery compiled by the first detective on the crime scene is expected to reach £3,000 at auction.
The 1963 heist was meticulously documented by Detective Constable John Bailey, from Bedgrove, Aylesbury, in a series of fascinating scrapbooks.
They give a blow by blow picture account from the crime scene to the capture and trial of the nine robbers.
Mr Bailey, a forensics officer, took hundreds of photos in the aftermath of the £2.6 million heist which saw the robbers hold up a Royal Mail train on a bridge near Cheddington.
After the investigation ended he was allowed to keep his incredible personal collection and used the four scrapbooks for lectures.
Mr Bailey, now 81, said: “I’m selling it because I’ve stopped giving talks and I’m sure someone else would like it. To me the robbery was just another crime and I had no idea at the time how famous it would become.
“I was called early in the morning and headed down there with my camera and powder for taking fingerprints.
“I used flash powder and took the picture with a cloth over my head and everything was upside down.
“I worked alongside the man from Scotland Yard and at one point we were both in the bath at the farm trying to get palm prints from the chrome hand rails.”
Chris Albury, of Dominic Winter auctioneers of Cirencester, said: “It is a unique and important archive and very collectable.”
The auction takes place on Wednesday, September 25.