The Swedish diplomat Raoul Wallenberg, who saved thousands of Jews during the second world war, has finally been declared dead by his homeland, 71 years after disappearing into the hands of the Soviet Union.

The announcement brings only a partial closure to one of the greatest mysteries of the cold war – the fate of a man nicknamed the Swedish Schindler – as his body was never returned to his family.

Nina Lagergren, half-sister of Raoul Wallenberg, with a picture of him. Photograph: Jonathan Nackstrand/AFP/Getty

As Sweden’s special envoy in Budapest during the war, Wallenberg’s actions allowed thousands of Jews to flee Nazi-occupied Hungary. Months before the war ended, the Soviets invaded Budapest and summoned the Swede to their headquarters in January 1945.

He disappeared, and his fate became a sensitive issue between the west and the Soviet Union.

“The official date of his death is 31 July 1952,” said Pia Gustafsson, an official from Sweden’s tax authority, which registers birth and deaths. “This date is purely formal. Legally, we must choose a date at least five years after his disappearance and there were signs of life until the end of July 1947.”

The decision came after a representative of Wallenberg’s family asked for a death certificate from Sweden, which published search notices for him and received no new information on his whereabouts.

A statement sent to AFP in 2015 by the family said Wallenberg’s “declaration of death is a way to deal with the trauma we lived through, to bring one phase to closure and move on”.

Wallenberg was sent by neutral Sweden to Hungary in 1944 and by early 1945 he had issued Swedish papers to thousands of Jews, allowing them to flee the country and likely death. The 32-year-old also acquired buildings – designated as Swedish territory – to house as many Jews as possible and provide them with extraterritorial status.

In 1957, the Soviet Union released a document saying Wallenberg had been jailed in Lubyanka prison, the notorious building where the KGB security services were headquartered, and that he died of heart failure on 17 July 1947. But his family refused to accept that version of events and for decades tried to establish what happened to him.

Wallenberg was showered with honours after his presumed death, including the Congressional gold medal by the US Congress and his designation by Israel as one of the “righteous among the nations” – individuals whose courage saved Jewish lives during the Holocaust.