Passage: In March 1991, parliament passed an amnesty law that pardoned all political crimes prior to its enactment. The amnesty was not extended to crimes perpetrated against foreign diplomats or certain crimes referred by the cabinet to the Higher Judicial Council. In May 1991, the militias (with the important exception of Hezbollah) were dissolved, and the Lebanese Armed Forces began to slowly rebuild themselves as Lebanon's only major non-sectarian institution.

Question: When was the amnesty law passed?
March 1991