In 1986, Duarte's tax reform plans, bitterly opposed by ARENA, were judged unconstitutional. In August, he participated in the historic Esquipulas II agreement with other leaders to lay the groundwork for a firm and lasting peace in Central America, outlining the demobilization of the guerrilla groups in El Salvador, Guatemala and Nicaragua. On October 5, 1987, a third dialogue began between the government and the FMLN, and on October 28, Congress passed an amnesty law, just two days after Herbert Anaya, the president of the special United Nations Human Rights Commission for El Salvador, was assassinated. Anaya's assassination was interpreted by some as a sign of disapproval of the peace process.