The United Nations is reopening the case of a plane crash that killed former Secretary-General Dag Hammarskjöld in 1961.

Hammarskjöld was on his way to what is now a part of Zambia to help broker peace between secessionist fighters in the Democratic Republic of Congo and U.N. troops who were trying to stabilize the newly independent country, the New York Times reports.

A three-person, independent panel appointed by Secretary-General Ban Ki-moon will have three months to investigate the evidence that has emerged since the U.N. first looked into the crash, according to a U.N. statement.

That evidence, the Times details, includes testimony from two U.S. intelligence officers stationed at listening posts hundreds of miles apart and who claimed they heard what sounded like the plane getting shot down; one recalled hearing “The Americans shot down the U.N. plane.”

The panel—made up of a jurist from Tanzania, a ballistics expert from Denmark and an aviation expert from Australia—is expected to submit a report to the Secretary-General no later than June 30.

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Write to Nolan Feeney at nolan.feeney@time.com.