WASHINGTON, D.C. — An expert witness testified to the “illegal” presence of a high-ranking U.S. military adviser who may have known about the plot to kill nearly 1,000 civilians who perished in El Mozote, El Salvador, nearly 40 years ago.

Terry Karl, a Stanford University professor and expert witness who has reviewed thousands of documents on the Dec. 11, 1981, massacre, said during the late-April and early May hearings in El Salvador that the presence of U.S. Sgt. Maj. Allen Bruce Hazelwood near the scene of the massacre was not only illegal, but knowledge of it would have brought U.S. military aid to the Central American nation to a halt.

In the 1980s, the U.S. largely funded the Salvadoran government’s involvement — to the tune of almost $1 million a day — in the war against armed-leftist rebels because it feared the formation of a communist bloc close to the United States.

U.S. Catholic leaders were vocal opponents of the aid, often lobbying Congress or protesting in Washington.

Officially, the war began in 1980 and ended with peace accords in 1992, although political strife had been brewing in El Salvador since the 1970s because of large-scale socioeconomic disparities.

Testimony in 2021 at the pretrial hearings affirmed what has long-been asserted by human rights advocates: That in fighting the war, the Salvadoran government made little distinction between rebels and poor, unarmed civilians, aiming to kill both.

Karl testified before a court in San Francisco Gotera that Hazelwood knew Lt. Col. Domingo Monterrosa, commander of the Atlacatl Battalion, which is infamous for wartime atrocities throughout the country, and he likely had knowledge of what was going to happen.

“The participation of an adviser (from the U.S.) in wartime activities is against our laws, and it was illegal at the time,” said Karl. Her testimony is particularly important given that El Salvador’s governments have failed to get the military to disclose its records, hindering prosecution of almost all major wartime atrocities committed during the conflict that left more than 70,000 Salvadorans dead, thousands disappeared but presumed dead, and forced many others to migrate.

Military authorities have refused Jorge Guzmán Urquilla, the judge hearing the case, access to records the institution might have on the mass killings in which its members participated. He also faced opposition in January by the archbishop of San Salvador, who initially blocked access to church documents; the prelate later reversed his position.

A monument in the hamlet of El Mozote, in the eastern part of the country, and the oral histories of families of the dead are about the only public acknowledgment of the massacre. Hundreds of children were buried in a common grave close to the monument, which lists the names and ages of some of the victims: Santos Argueta, 15; a toddler with the last names Vigil Marquez, 2; Catalino Rodriguez Guevara, 70.

The hearing also revealed that the United States knew Salvadoran forces used napalm against the population, even though the incendiary gel, which burns the skin, was banned for use against civilians by the United Nations in 1980.

Karl’s testimony also included the role of clandestine help from the U.S., which included “disgruntled Vietnam veterans” who worked as mercenaries in El Salvador, providing financing and helping the infamous battalion “fight communism.”

More witnesses are expected to testify.