A Moscow court on Monday rejected a suit against the Russian security services from the family of Raoul Wallenberg, the famous Swedish diplomat who disappeared 70 years ago, RBC reports.

Wallenberg helped rescue thousands of Hungarian Jews during World War II before Soviet forces captured him in 1945, reportedly on suspicions of espionage, and transported him to the KGB’s Lubyanka Prison.

He is believed to have died in the summer of 1947 but his death is still shrouded in mystery.

In July, Marie Dupuy, Wallenberg’s nice, filed a lawsuit in Moscow against the KGB’s successor, the Federal Security Service (FSB), seeking access to documents she believed could shed light on Wallenberg’s fate.

The case was dismissed by the Meshchansky Court on Monday, the family’s attorney Darya Sukhikh told RBC.

Ivan Pavlov, Dupuy’s lawyer, said the family planned to appeal the court’s decision, which he characterized as “unlawful.”

“The fate of Wallenberg is one of the biggest mysteries in Russian history,” he was quoted as saying by the Interfax news agency. “The documents requested by Wallenberg’s relatives are already 70 years old and access to them should be opened.”