UP, and determining the sociopolitical stance of the urban peasantry. The UP performed better in elections than any other leftist party in Colombia's history. In 1986, UP candidates won 350 local council seats, 23 deputy positions in departmental assemblies, 9 seats in the House, and 6 seats in the Senate. The 1986 Presidential candidate, Jaime Pardo Leal, won 4.6% of the national vote. Since 1986, thousands of members of the UP and other leftist parties were murdered (estimates range from 4,000 to 6,000). In 1987, the President of the UP, Jaime Pardo, was murdered. In 1989 a single large landholder had over 400 UP members murdered. Over 70% of all Colombian presidential candidates in 1990—and 100% of those from center-left parties—were assassinated. Gaviria and Samper presidencies (1990–1998) During this period, the Colombian government continued its negotiations with the FARC–EP and other armed groups, some of which were successful. Some of the groups which demobilized at this time include the EPL, the ERP, the Quintín Lame Armed Movement, and the M-19. On 10 August 1990, senior leader Jacobo Arenas, an ideological leader and founder of FARC–EP, died of a heart attack at the Casa Verde compound in Colombia's eastern mountains. Towards the end of 1990, the army, with no advance warning and while negotiations were still ongoing with the group, attacked and seized four linked bases. The last of these a compound known as Casa Verde, which housed the National Secretariat of the FARC–EP, was seized on 15 December 1990. The Colombian government argued that the attack was caused by the FARC–EP's lack of commitment to the process, demonstrated by continuing its criminal activities and FARC attacks in November. On 3 June 1991, dialogue resumed between the Simón Bolívar Guerrilla Coordinating Board and the government on neutral territory in Caracas, Venezuela and Tlaxcala, Mexico. However, the war did not stop, and armed attacks by both sides continued. The negotiation process was broken off in 1993 after no agreement was reached. The Coordinating Board disappeared not long after that time, and guerrilla groups continued their activities independently. Before the break off of dialogue, a letter written by a group of Colombian intellectuals (among whom were Nobel laureate Gabriel García Márquez) to the Simón Bolívar Guerrilla Coordinating Board was released denouncing the approach taken by the FARC–EP and the dire consequences that it was having for the country. In the early 1990s, the