“To allow the musicians to continue to work was also a way to control them better,” said the 44-year-old Italian Jew. “At Auschwitz, there were seven orchestras.”

Lotoro has amassed some 4,000 pieces, all composed between March 1933, when the Nazis’ Dachau death camp was opened soon after Hitler won absolute power, and the end of World War II in 1945.

But while much is from Nazi camps, Lotoro’s collection covers internment camps from both sides of the war.

“I’m collecting all the music, written not just in Europe but also in Asia: Jewish religious songs, hymns by Dutch Quaker pastors, gypsy songs or those of an American, Edmund Lilly, held in a camp in the Philippines, and ballads by Italian soldiers held by the Allies,” he said.

Carefully archived in Lotoro’s office in Barletta, southern Italy, much of the music has never been recorded.

The son of distinguished Czech composer Rudolf Karel, who died at the Theresienstadt camp near Prague in 1945, gave Lotoro a photocopy of a five-part composition written on toilet paper.

In a music shop in Prague, Lotoro met Eliska Kleinova, the sister of Gideon Klein, who was the organizer of cultural life at the Theresienstadt concentration camp in the Czech Republic and died in the gas chambers of Fuerstengrube.

Lotoro, himself an accomplished musician who studied under the celebrated French pianist Aldo Ciccolini, took home the music to a sonata Klein composed at Theresienstadt, whose Czech name is Terezin.

“I started studying it. There were a lot of mistakes. I corrected them, recorded it and sent it to Eliska. She was thrilled. It was a very difficult piece,” Lotoro said.

At the camp, musicians were allowed to play a piano for half an hour a day, which may explain anomalies in some pieces.

“The piano lost some of its reality,” said Lotoro, who sports a black beard and small round glasses.

“The musician composed in his head, and the physical limits of the instrument didn’t exist anymore. These pieces reflect a special sort of ventilation.”