In 1985, seven American hostages were taken by a hostile group in Lebanon which had ties to Iran. As an exchange for the hostages, the U.S. National Security Council, under President Ronald Reagan, sold arms, which were under embargo at the time, to Iran. The Lebanese released all but two hostages.
Later, the U.S. Government used the profits from the sale of the arms to fund the Contras, an anticommunist rebel group in Nicaragua.
In 1986, an Iranian leak led to an investigation which involved 41 days of Congressional hearings. The Reagan administration refused to declassify certain documents for Congress for the investigation. The administration denied involvement in the affair, and the extent of their involvement is unclear.
The investigation did not determine that the sale of weapons to Iran was a criminal offense. Some officials, however, were charged for financially supporting the Contras.