In 1953, the CIA orchestrated a coup d'etat against the democratically elected government of Iranian Premier Mohammad Mossadegh, installing Shah Reza Pahlavi.

It's no secret that the CIA did it, and the US has admitted it time and again, but the State Department has announced it is once again delaying the release of its study on the coup, claiming the admission would undermine "ongoing negotiations with Iran."

The coup was carried out primarily for the benefit of British oil interests, as Mossadegh was planning nationalization. Legally speaking, the State Department was only supposed to keep the history secret for 30 years.

It's hard to imagine anything in the history of the coup is unknown, let alone that it could do any further harm to US-Iranian relations after decades of acrimony. Still, the lure of secrecy seems to be winning out among officials, as usual.