In a makeshift courtroom on the second floor of a nondescript brick building in northeastern El Salvador, Judge Jorge Guzmán has spent the last six years painstakingly gathering evidence from the survivors of one of the worst massacres in the modern history of Latin America: the slaughter of a thousand old men, women and children by the Salvadoran army during the country’s civil war.

Forty years after the massacre, former senior military officers, including the minister of defense at the time, have been facing charges ranging from kidnapping and rape to murder. The military and the Salvadoran elite have repeatedly sought to block any accountability for the massacre, and the current president, Nayib Bukele, a 40-year-old right-wing populist who is often compared to Donald Trump and reminds some of Hungary’s Viktor Orban, may have just succeeded. He has made no secret of his desire to terminate the investigation.

On Aug. 31, the legislature, controlled by Bukele’s party, fired every judge in the country older than 60. Guzmán is 61. Within El Salvador, the prevailing view is that one of the aims was to end the investigation.

Bukele’s decimation of the judiciary is his latest move to increase his power and presents a challenge to the Biden administration. “Human rights will be the center of our foreign policy,” the U.S. president declared in a speech on the same day, announcing the end of the Afghan war. It will be achieved through diplomacy, he said, not military might. The United States has had a long and complicated relationship with El Salvador for the past four decades, and it is not clear what sanctions Washington is prepared to invoke.

Bukele is not likely to buckle easily. In May, after the Supreme Court overturned several of his executive orders, the legislature dismissed five justices and replaced them with loyalists. In response, Vice President Kamala Harris tweeted that the United States had “deep concerns about El Salvador’s democracy.” Bukele answered with a string of tweets: “With all due respect,” he wrote, “we’re cleaning our house and this isn’t your responsibility.”

On Sept. 3, El Salvador’s Supreme Court ruled that Bukele may run for reelection in 2024, despite a term-limits provision in the constitution. He also touched off another controversy last week by adopting bitcoin as an official currency; since 2001, it has been the U.S. dollar. Many observers believe that this move is designed to cushion El Salvador’s economy in the event the Biden administration imposes financial sanctions.

The U.S. State Department condemned the “decline in democratic governance” in El Salvador and called on Bukele to respect “the separation of powers and the rule of law.”

The assassination in March 1980 of the country’s revered Roman Catholic prelate, Archbishop Oscar Arnulfo Romero, by a right-wing death squad touched off a simmering revolution. Several leftist guerrilla and political organizations united under the banner of the Farabundo Marti National Liberation Front (FMLN) to bring to an end decades of rule by an alliance of the oligarchy and military. In the name of stopping the spread of communism, the United States backed the government, with hundreds of millions of dollars in economic and military aid.

In December 1981, the Atlacatl, a Salvadoran army battalion, pillaged, plundered and raped its way through El Mozote and several other peasant villages in the northeastern part of the country. The soldiers summoned villagers to the square and forced them to lie face down in the dirt. The old men were taken away, tortured for information about whether their sons had joined the guerrillas and then executed. Women were raped and executed. A few women with infants, along with adolescents, were forced into the convent behind the Roman Catholic Church. The soldiers fired on them and threw grenades. A forensic exhumation years later found the bodies of at least 143 individuals, 90% of them under the age of 12; their average age was 6.

The massacre was exposed by reporters from The New York Times and The Washington Post who arrived on the scene with a photographer weeks after it occurred. There were still bodies in the cornfields and in mud houses being chewed over by vultures. The Reagan administration denied that government troops had carried out the massacre. The American Embassy in El Salvador suggested that the guerrillas were to blame, and the administration’s conservative supporters claimed it was “guerrilla propaganda.” Classified U.S. documents released by the Clinton administration confirmed the role of the Atlacatl battalion.

The struggle for justice on the part of the survivors and the relatives of the victims has been arduous, marked by defeats, victories and more defeats. In 1991, the legal aid office of the Roman Catholic Church petitioned the court to conduct an investigation. When the court asked the Ministry of Defense for the names of the officers in charge of the operation, it was told “no information” about any “supposed operation” could be found.

Two years later, a peace agreement ended the decade-long civil war, and a United Nations Truth Commission concluded that the government was responsible for at least three-quarters of the 75,000 civilians killed during the war. Acting quickly, and without hearings, the National Assembly, controlled by the right-wing political parties, passed a sweeping amnesty law.

The victims challenged the law in the Salvadoran Supreme Court. They lost. In 2011, they filed a case with the Inter-American Court of Human Rights. In its 152-page opinion, the court said there was no dispute that “the Armed Forces executed all of those persons it came across: elderly adults, men, women, boys and girls, they killed animals, destroyed and burned plantations, homes, and devastated everything community-related.” As for the amnesty law, the court found that it was in contravention of the Salvadoran government’s “international obligation to investigate and punish the grave human rights violations relating to the massacres of El Mozote and nearby places.”

Armed with this decision, the victims went back to the Salvadoran Supreme Court. In 2016, it ruled the amnesty law invalid. Guzmán reopened the investigation and began taking testimony from survivors. (Although the case is often referred to as a trial, it is roughly the equivalent of what in the United States is called a preliminary inquiry, at the end of which Guzmán can either dismiss the charges or recommend that the men be criminally prosecuted.) Because Guzmán is one of the only judges in the region and has had a heavy load of civil and criminal cases, the El Mozote investigation has proceeded slowly.

Amadeo Sanchez told the judge that he was 8 at the time of the massacre and had survived by fleeing into corn and sisal fields with his father. They heard the shooting and screams of young girls being raped. When Sanchez returned to the village, he found the bodies of his mother and two siblings as well those of aunts, uncles and cousins. In one adobe house, he testified, he saw the body of a woman who had been shot in the head. Next to her was a 1-day-old boy. His throat had been cut, Sanchez told the judge, making a slicing motion with his hand. On the wall, soldiers had scrawled, “Un niño muerto es un guerrillero menos” — “One dead child is one less guerrilla.”

Another witness, Maria Rosario, told the judge that 24 members of her family had been killed, including her mother. When she testified, she looked at the defendants, who were sitting on folding chairs in rows. She wanted to scream “assassins,” she said in a 2018 interview. “But I couldn’t allow myself to do that because the judge was right in front of me. You just endure the pain that you feel.”

Bukele has been as determined as his predecessors and the military high command to quash the investigation. When Guzmán sought to execute a search warrant at military bases for documents pertaining to the massacre, Bukele ordered the armed forces not to comply; soldiers were stationed at various bases to block the judge’s entry. In a televised address to the nation last year, Bukele accused Guzmán of being a member of the FMLN, which has become a political party since the peace agreement. The claim is baseless.

He also accused the victims’ lawyer, David Morales, of becoming a millionaire from his representation. The 55-year-old Morales began seeking justice for the victims when he was an intern in the legal aid office of the Roman Catholic Church; he now works for a nongovernmental human rights organization, Cristosal. Morales, who has finished presenting witnesses to the court, said that, before Bukele’s dismissal of the judges, he had expected a ruling by Guzmán to be imminent. But unless domestic and international pressure forces Bukele to reverse his order, Morales now fears that the investigation is over.