Towards the end of 1990, the army, with no advance warning and while negotiations were still ongoing with the group, attacked a compound known as Casa Verde, which housed the National Secretariat of the FARC–EP. The Colombian government argued that the attack was caused by the FARC–EP's lack of commitment to the process, since the organization was continuing its criminal activities. On August 10, 1990 senior leader Jacobo Arenas, an ideological leader and founder of FARC–EP, died of a heart attack. On June 3, 1991 dialogue resumed between the 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. Beginning in 1996, FARC–EP began applying a new military strategy involving multi-front attacks on military objectives, and the use of both 61mm and 80mm mortars and of homemade mortars known as "cylinder bombs" (the use of which has been condemned by many, due to their inaccuracy and potential for causing collateral damage). This resulted in a series of major military victories over Colombian government forces. On August 30, 1996, the FARC–EP staged a surprise attack on a Colombian military base in Las Delicias, Putumayo. Within 15 hours, the base had been completely destroyed, w/ 54 Colombian soldiers killed, 17 wounded, and 60 taken hostage. The 60 hostages were released in June 1997. In March 1998, in southern Caquetá, with the help of local sympathizers and informants, FARC–EP forces annihilated an elite Colombian army unit, the 52nd counterguerrilla battalion of the 3rd Mobile Brigade. A force of 600–800 guerrillas attacked the battalion, and by the end of the engagement, 104 of the battalion's 154 men had been killed. In November 1998, FARC–EP forces overran the provincial capital Mitú, located in Vaupés near the border with Brazil.