Corps was created to carry out extralegal operations alongside the SCUGA. The Fourth Corps was an illegal fifty-man assassination squad which operated in secrecy from other members of the National Police, taking orders from Col. Sosa and Col. Arriaga. Links with the Phoenix Program During the period of counterinsurgency and police militarization under Col. Sosa Avila, the PN worked closely with the USAID Office of Public Safety (OPS), which largely operated as a front for the CIA. Between 1966 and 1974, the OPS help militarize the PN and provided extensive training to Guatemalan security services in areas of counterinsurgency, intelligence gathering and interrogation. By 1970, more than 30,000 Guatemalan police officers had received some form of OPS training. US government Biographic Register and Foreign Service Lists reveal that many of the same American OPS and other functionaries operating in Guatemala were also involved in Vietnam, particularly in Civil Operations and Revolutionary Development Support (CORDS). When asked about the origins of the death squads in Guatemala in a subsequent interview, General Oscar Humberto Mejia Victores (military president from 1983 to 1986) stated that they were initiated "in the 1960s with the CIA". 1970s In 1970, after the fraudulent election of Col. Arana Osorio (representing the MLN-PID), the security forces engaged in harsher counterinsurgency measures in Guatemala City. From a special telecommunications annex of the presidential palace, the new military government coordinated a "covert program of selective assassination". The Arana presidency was one of the bloodiest regimes in modern Latin-American history, with Amnesty International estimating that at least 15,000 Guatemalans were killed or "disappeared" between 1970 and 1973. During his four-year term as military president, Arana continued to strengthen coordination among the security structures. As high-ranking intelligence officer Col. Otto Perez Molina (later president from 2012 to 2015) stated in a 1993 interview, the Arana-period marked the beginning of a period of "good intra-group relations and the most successful in combating urban insurgency". In the 1974 election of Gen. Kjell Eugenio Laugerud Garcia, MLN party leader Mario Sandoval Alarcon - one of the CIA's most important assets in Guatemala - was appointed Vice-President of the Republic. The election of Gen. Laugerud Garcia marked the beginning of a period of strained relations between the Guatemalan government and the United States. This was primarily due to tensions between Guatemala and the UK over the sovereignty of Belize (formerly British Honduras) and US Congress's criticism