On December 2, 1980, four American churchwomen were beaten, raped and murdered in the countryside 15 miles from the country’s international airport.
This was a huge problem for the governments of the U.S. and El Salvador because four religious missionaries who were U.S. citizens had been brutally raped and murdered and because there was a huge public outcry in the U.S. for investigation and prosecution of those responsible. Continuation of U.S. military aid to El Salvador was also at risk. Immediately after the discovery of the murders, President Carter suspended $25 million of aid (with restoration 10 days later), and in 1983 Congress voted to withhold $19 million in aid pending a verdict in the criminal case discussed below.
There were five non-judicial investigations of the crime.
The first investigation was initiated on December 6, 1980 (four days after the murders), by President Jimmy Carter, when he appointed William G. Bowdler, a State Department official, and William D. Rogers, a former Department official, to go to El Salvador and investigate the case. They went and said they had found no direct evidence of the crime or of involvement of Salvadoran authorities, but that there had been a cover-up of the murders.
The Junta then governing El Salvador started the second investigation by putting Colonel Roberto Monterrosa in charge of an official commission of investigation. Later he admitted that his commission had excluded the possibility that Salvadoran security forces had been involved in the crime because that would have created serious difficulties with those forces. He hid from the U.S. Embassy evidence implicating a deputy sergeant of the Salvadoran National Guard. In short, Monterrosa did not conduct a thorough, honest investigation.
Simultaneously with the Monterrosa commission, the Director-General of the National Guard, Carlos Eugenio Vides Casanova, started a third investigation. He put Major Lizandro Zepeda in charge. Zapeda reported there was no evidence that National Guard personnel had committed these crimes while he simultaneously ordered the actual Guard perpetrators to replace their rifles to avoid detection and to remain loyal to the National Guard by suppressing the facts. There is also evidence that Zapeda kept his superior, Vides Casanova, informed of the details of the investigation.
The fourth investigation was conducted by former U.S. federal judge Harold R. Tyler, Jr. at the appointment of the U.S. Secretary of State. He concluded that the purpose of the Monterrosa and Zapeda investigations had been to establish written precedents clearing the Salvadoran security forces of blame for the crimes. Tyler also concluded that senior officers had not been directly involved in the crimes themselves although it was quite possible that General Vides Casanova, who had been the commander of the National Guard at the time and was then the Salvadoran Minister of Defense, was aware of the cover-up. Indeed, the deputy sergeant immediately had confessed his involvement to his superiors, who kept this secret and took other steps to make detection more difficult. 
In December 1981 Colonel Vides Casanova appointed Major Jose Adolfo Medrano to conduct a fifth investigation.
As the first four of these investigations were proceeding, the Salvadoran government announced that it had sent to the FBI for analysis new evidence, including fingerprints of Salvadoran police and military personnel who had been stationed in the area of the national airport on December 2. Subsequently there were reports in late April 1981 that the FBI had concluded that certain evidence pointed to six Salvadoran National Guardsmen as the killers.
Several weeks after this report about the FBI conclusions, six Salvadoran Guardsmen were arrested to start a Salvadoran judicial investigation and eventual prosecution of this crime. The next post in this series will look at this judicial investigation and prosecution.
 See Post: The Four American Churchwomen of El Salvador (Dec. 12, 2011); Post: The December 1980 Murders of the Four Churchwomen in El Salvador (Dec. 14, 2011).
 Commission for the Truth for El Salvador, Report: From Madness to Hope: The 12-year war in El Salvador at 65 (March 15, 1993), http://www.derechos.org/nizkor/salvador/informes/truth.html [Commission Report]; Chavez, 5 Salvadorans Are Found Guilty in Slaying of U.S. Churchwomen, N.Y. Times (May 25, 1984).
 Onis, U.S. Officials Fly to El Salvador to Investigate Murders, N.Y. Times (Dec. 7, 1980); Commission Report at 63. Bowdler was Assistant Secretary of State for Inter-American Affairs and a former U.S. Ambassador to El Salvador (1968-71). In the Ford Administration Rogers served as Assistant Secretary of State for Inter-American Affairs and Under Secretary of State for Economic Affairs.
 Commission Report at 63-64.
 Id. at 63-65; Bonner, Cover-Up Charged in Death of Nuns, N.Y. Times (Feb. 16, 1984).
 Commission Report at 64.
 Schumacher, Salvadoran Discloses New Evidence in the Murder of Four U.S. Missionaries, N.Y. Times (Mar. 14, 1981); Assoc. Press, Link of Salvadoran Soldiers to Killing of 4 Reported, N.Y. Times (April 27, 1981).