In the decades since the death of United Nations Secretary General Dag Hammarskjold, his native Sweden has led the call for countries to disclose what they know about the air crash in central Africa that killed him — one of the most abiding mysteries in global diplomacy.

The Swedish authorities, however, have themselves refused a prominent researcher’s request for access to official Hammarskjold-related documents on grounds that they are classified under national security laws.

The decision, handed down by Sweden’s national archives on July 11 to a researcher, Hans Kristian Simensen, has raised questions about what the documents contain. It also seems to undermine Sweden’s stance that nations like the United States, Souith Africa and Britain should stop stonewalling requests for information.

“How can Sweden expect other countries to declassify relevant documents if Sweden is not doing the same?” the descendants of some of the 16 people killed in the crash asked in a letter to Sweden’s Foreign Ministry and a leading Swedish newspaper, Dagens Nyheter.