US GI John Pistone never knew the significance of the heavy, green leather-bound volume titled "Picture Gallery Linz XIII", but took it as a memento from Hitler's mountain home in Berchtesgaden in 1945.
But a washing machine contractor, an amateur history buff, spotted the book on a shelf at Mr Pistone's home near Cleveland, Ohio, and made his own checks on the internet.
He contacted a Dallas-based group, Monuments Men Foundation for the Preservation of Art, that had been involved in the restitution of two other similar albums. Robert Edsel, its founder, went to Ohio and realised the significance of the book.
Hitler, an art school reject who long harboured his own ambitions of becoming a great painter, was obsessed with his art collection, lecturing his staff each night even as the Allies were closing in on Berlin.
Every Christmas and birthday, he was presented with an album collection cataloguing looted Nazi art that he planned to install in a "Fuhrermuseum" he had designed for his hometown of Linz in Austria.
Hitler envisioned the museum rivalling those in Dresden and Munich, and had helped draw up architectural plans, which eventually grew to include a theatre, an opera house and a hotel. In all he was presented with 31 albums. Photographs show him working on plans for his museum, while a model of Linz was moved to his bunker in Berlin.
Volume XIII, Mr Pistone's album, contains reproductions of 19th-century German and Austrian pictures, the art Hitler admired most as it showed his "Volk", or countrymen, in heroic poses and the landscapes as an Aryan idyll. The artwork is by mostly obscure artists, whose work Hitler would have been able to identify with.
On Tuesday, Mr Pistone presented the book to the German Historical Museum in Berlin, which has 20 more Linz albums and described the volume as a "valuable cultural work".
The remaining 11 are still missing, likely also looted by American soldiers who never knew what they had taken.
"It was just a book full of pictures of old paintings to me," said Mr Pistone, 88. "I just wanted something that proved I had been on Hitler's mountain."
"I never bought the paintings that are in the collections that I built up over the years for my own benefit but only for the establishment of a gallery in my hometown of Linz," he wrote in his last will and testament before he committed suicide in his bunker in April, 1945.
Nazi henchmen and art dealers bought and stole thousands of paintings, sculptures, tapestries and other objects from private collections across Europe, stockpiling them in secret locations until the museum was built.
Much of the art was recovered from salt mines and warehouses at the end of the war, but the 31 volumes of reproductions were taken by Allied troops.