Efrain Rios Montt seized power in a military coup in 1982 and during his 17 month reign killed anywhere between 10,000-20,000 people and destroyed 600 villages, in a campaign to reduce the Mayan population, who he claimed were naturally susceptible to communism due to their immaturity (his words), in the bloodiest part of the Guatemalan genocide.
Anyway, in 1982 and 1983 Rios Montt's army received millions of dollars in United States aid, which had been suspended by Carter was resumed by Reagan, claiming that the human rights situation was being improved by the new regime. He also provided propaganda support to the genocidaires, personally flew down to Managua in December of '82 to meet with Rios Montt, giving him a big photo op and giving an glowing interview where he calls him a man of great integrity and commitment who was committed to democracy (NB, Montt was a general installed by military coup) and was getting a bum rap. In case you are thinking this is a mistake, declassified CIA documents in Fed of 82, shortly before Rios Montt's coup, reports that the army was conducting massacres in a specific Mayan province, was meeting no substantial resistance, and that the army considered all Ixil (an indigenous) tribe to be insurgents and were giving no quarter, so he knew that 'fighting guerillas' was code for killing Mayans, and in February of 83, noted the rise in right wing violence and that bodies were piling up in rivers and gullies in the countryside. His financial support for the regime continued until it fell and through Mejia Victores (also convicted of genocide) regime.
Please expand your scope to include the even more murderous predecessor to Rios Montt, Romeo Lucas Garcia. Who also got support from the Reagan administration, for that matter.