Netherlands ? Anne Frank’s cousin on Monday donated thousands of letters, photographs and documents that archivists say will reveal details about the background of the teenage diarist who became a symbol of the Holocaust.

Bernhard “Buddy” Elias, 82, had kept the materials for decades in his Swiss attic before permanently loaning them to the Anne Frank House – the Amsterdam museum incorporating the tiny apartment where the family hid during the Nazi occupation of the Netherlands – to mark Monday’s 60th anniversary of the first publication of “The Diary of Anne Frank.”

The donation includes Otto Frank’s 1945 letter informing his mother in Switzerland that his daughters, Anne and Margo, and his wife, Edith, died in Nazi concentration camps; the letter his mother wrote responding to diary excerpts that Otto sent her; and photographs from the late 1890s of the Frank family in its native Frankfurt, Germany.

With Elias’ collection, the museum now holds nearly all known historical material about the family, including the postwar years when Otto Frank – the only survivor – compiled and promoted the diary.