An archive of Holocaust evidence long closed to public view has been made available in London for the first time since the 1940s, when it was used by the United Nations’ War Crimes Commission.

The vast UNWCC trove of documents, most of which were smuggled out of Eastern Europe during the early 1940s and later used to convict leading Nazis, are being opened at the Wiener Library this week.

Until now, only researchers with special permission from their governments and the UN were able to view them, and even then they were not allowed to take copies.

It shows how Britain, the U.S. and Russia were slow to press for leading Nazis to face trial for crimes against humanity, with countries such as Poland leading the call.

In another bundle of documents built up to indict Adolf Hitler for war crimes in Czechoslovakia, there is an affidavit from British soldier Harry Ogden, who was imprisoned in a prisoner-of-war camp next to Auschwitz-Birkenau.

The release shows how the Polish government in exile was able to provide extraordinary detail of the camps in which Jews and others were held and killed, with one 1944 description documenting how victims were forced to strip and how “the terracotta floors in the chambers… became very slippery when wet”.

The London library was originally founded in the Netherlands and is named after Alfred Wiener, who shipped his collection to the UK in 1939, subsequently working with British authorities to chart the crimes of the Nazi government.

Archivist Howard Falksohn said the release meant scholars “may be able to rewrite crucial chapters of history using the new evidence”.

The online release has been timed to coincide with the launch of ‘Human Rights After Hitler,’ a book by Dan Plesch, a London-based researcher who has had access to the archive for ten years. He helped convince diplomats to open access.

Plesch describes how the changing geopolitical landscape of the late 1940s meant that prosecuting Nazis became less important than rallying support for America’s anti-Communist offensive at the start of the Cold War.