(JTA) — Raoul Wallenberg, the Swedish diplomat who saved thousands of Hungarian Jews from the Nazi gas chambers, was executed in a Soviet prison, according to a KGB head’s diaries. The diaries of Ivan A. Serov, who ran the former Russian secret police and intelligence agency from 1954 to 1958, were discovered inside the walls of his second home in northwestern Moscow, which his granddaughter is now renovating. Discovered four years ago, the diaries were published this summer, The New York Times reported Sunday. “I have no doubts that Wallenberg was liquidated in 1947,” Serov wrote.

The diaries contains references to several previously unknown documents referring to Wallenberg, including one recording the cremation of his body. They were published under the title Notes From a Suitcase: Secret Diaries of the First KGB. Chairman, Found Over 25 Years After His Death, which went for sale in Russia in June. Serov died in 1990 at age 84. He is thought to have hidden the diaries around 1971. A 1991 joint Russian-Swedish effort to discover what happened to Wallenberg yielded no definitive conclusion when it ended in 2000. Wallenberg disappeared in 1945 after being seen surrounded by Soviet officers in Budapest. The Soviets later claimed Wallenberg had died of heart failure in prison. The diplomat’s parents both reportedly committed suicide in 1979 in despair over his disappearance. In November 2015, Wallenberg family members asked Swedish authorities to declare him dead.