Sept. 30, 4:23 p.m.: This story has been clarified.

Editor's Note:This story has also been published in Spanish.

RIVERSIDE, Calif. — Shaken by sobs, his head bowed, a former Guatemalan commando testified last week that he wept as he hurled a little boy to his death in a village well 31 years ago while a commanding officer, Lt. Jorge Vinicio Sosa Orantes, snarled: “This is a job for men!”

Sosa, now a 55-year-old U.S. citizen, watched that grim testimony from a defense table guarded by U.S. marshals in a federal courtroom here. His former comrade-in-arms, Gilberto Jordán, accused Sosa of playing a lead role in one of the worst war crimes in the recent history of the hemisphere: the massacre of 250 people in the Guatemalan hamlet of Dos Erres in 1982. Sosa is charged with fraudulently obtaining U.S. citizenship years later by concealing his participation in the massacre.

The trial began last week and is the first trial in the United States involving an atrocity from Guatemala’s 30-year civil war. It is also the first full airing of the Dos Erres case in a U.S. court. Sosa has become the highest-ranking suspect to be prosecuted. U.S. authorities had previously jailed Jordán, who pleaded guilty to immigration fraud charges in 2010, and another ex-soldier who had migrated to the United States. Guatemalan courts have convicted five former commandos. Seven others remain fugitives in an ongoing case that has tested Guatemala’s ability to pursue justice against war criminals shielded by corrupt security forces and powerful mafias.

During the first four days of the trial, federal prosecutors undertook an unusual challenge: attempting to prove Sosa participated in the slaughter to convict him of the relatively minor crime of immigration fraud. When Sosa obtained citizenship in 2008 and a green card in 1998, he allegedly made false statements on immigration forms by failing to disclose his military service and saying he had never committed a crime for which he had not been arrested, according to prosecutors.

The defense argues that Sosa did not think he had committed a crime because he had been a soldier following orders. Sosa’s lawyer also asserted that the questions on the immigration forms were vague and that U.S. immigration officials should have seen in Sosa’s file that he had disclosed his Guatemalan military service in a failed application for political asylum in 1985.

“This case is about an ex-soldier’s answers on an immigration form, pure and simple,” said the lawyer, H.H. (Shashi) Kewalramani, during opening arguments. “As much as the U.S. government wants to make this a war crimes case, it’s not.”

It certainly resembles a war crimes case, however. The testimony in this city an hour east of Los Angeles plunged the jury into the horror in a Guatemalan jungle village three decades ago. Two former commandos recounted a rampage of rape and murder that wiped Dos Erres off the map. A survivor who was a boy in 1982 described clinging to his mother’s leg as soldiers dragged her to her death. And Sosa’s ex-wife and the lead investigator testified that Sosa fled to Mexico and then Canada three years ago after federal agents served a search warrant on his Riverside County home.

Canadian police arrested Sosa, who holds Canadian as well as U.S. citizenship, in 2011 and extradited him to the United States last year.

The testimony began with a dramatic reunion between Sosa and Jordán, who is serving a 10-year prison sentence in Florida. In 1982, both worked as instructors at a school that trained “Kaibiles,” as Guatemala’s notoriously brutal commandos are known. As the civil war intensified, the regime of dictator Efraín Ríos Montt reassigned the instructors to a 20-man rapid reaction squad.  Four were lieutenants—Sosa had the least seniority among them—and the rest were sergeants.

Sosa is a compact, black-mustached martial arts expert. He spent the decade before his 2010 indictment operating karate schools in Southern California. Wearing a dark suit and glasses, he watched last Tuesday as federal marshals brought in Jordán, who wore orange prison overalls and leg chains. The two veterans did not acknowledge each other.

Jordán looked older than his 57 years: bespectacled, gray-haired, tormented. In 2010, he confessed his involvement in the massacre when federal agents went to his home to question him. He told the agents he had known the day would come when he would have to pay for his actions. He faces deportation to stand trial for mass murder in Guatemala upon his release.

Jordán testified in Spanish through an interpreter. He said he has received no deal other than a promise that U.S. prosecutors will write a letter to Guatemala’s attorney general saying he has cooperated.

The initial goal of the mission on Dec. 6, 1982, was to recover 21 rifles that guerillas had taken during an ambush on soldiers, Jordán testified. Intelligence indicated that the rifles were in Dos Erres, but Jordán said the squad found no rifles or guerrillas and encountered no resistance from the peaceable citizens of the hamlet. The commandos separated the men from the women and children and herded the two groups into a church and a school. The nightmare began when a lieutenant raped one of the women, Jordán said. After a meeting among the lieutenants, new orders were given, Jordán testified.

“The mission changed,” he said. “They ordered us to kill all the people.”

Jordán was a seasoned paratrooper at the time, but he had not yet become a Kaibil. He portrayed himself as an unwilling participant in the slaughter. He testified that he was ordered to bring a child and throw him into a well in the center of the village that became the epicenter of the massacre.

“He was about 3 years old, the age of my son,” Jordán testified.

Jordán bent forward in the witness stand and wept as he continued, staring straight down. He said: “As we were on our way, I was crying. He was staring at me and crying as well. A sergeant told me not to cry or I would end up in the well … I arrived and that’s when I heard Mr. Sosa, and he said this was a job for men and I threw the child in the well.”

Assistant U.S. Attorney Brian D. Skaret asked how Jordán felt at that moment. Jordán lifted his head and snapped: “Bad!”

The testimony of Jordán and another ex-commando, César Franco Ibañez, placed Sosa at the edge of the well supervising the methodical extermination of the villagers. The commandos blindfolded their victims, questioned them, slammed them on the head with a metal sledgehammer and dumped them into the well, according to the testimony. Both witnesses testified that a man who had fallen onto the pile of victims insulted Sosa, and the enraged lieutenant fired his gun into the well. Jordán testified that Sosa also tossed a grenade in the well.

“I think he lost his head and started firing,” Franco testified. “He answered them with his rifle … He said: ‘Well die, you sons-of-bitches.’ ”

Franco remained impassive when he testified about killing people and raping a woman. The short, stocky former sergeant is one of two members of the squad who broke the military’s code of silence in the mid-1990s   and gave unprecedented first-hand testimony. Guatemalan prosecutors made Franco a protected witness and relocated him another country, where he lives today with his family. The Guatemalan government pays him a $550 monthly stipend, he said. He has testified in previous U.S. and Guatemalan prosecutions and given interviews to news organizations, including ProPublica.

During cross-examination, the defense attorney tried to cast doubt on Franco’s testimony, asserting that his story has changed over the years about details such as whether Sosa used a rifle or a shotgun. Kewalramani cited a prosecution report about an interview of Franco by U.S. investigators, saying Franco had not mentioned Sosa in a list of commandos at the village well during that interview in a U.S. embassy in the country where he lives.

Franco insisted that the report was wrong.

“I also mentioned Sosa,” Franco testified. “… I named him since the very beginning.”

Another challenge to Franco’s testimony arose from an unexpected source Friday morning. Prosecutor Skaret disclosed in court that the section chief of the Justice Department’s war crimes unit had received an email from a prosecutor who is on leave. The prosecutor, George Ferko, wrote in the email that he had read about Franco’s testimony in news reports and was compelled to alert his colleagues that he felt the witness was not credible, according to Skaret. Ferko had interviewed the ex-commando as part of an investigation in 2009, Skaret said.

“César is a liar,” Ferko wrote, according to Skaret’s statement in court. “César has changed his story once again.”

As a result, Sosa’s attorney said he wanted an opportunity to talk to Ferko to decide whether to call him as a witness. The episode was remarkable: It is highly unusual for a Justice Department prosecutor to raise questions about a witness being used by his colleagues in the middle of a trial.

Nonetheless, the development may not have much impact. The defense has not challenged the central point of the testimony by the two former Kaibiles: that Sosa took part in the Dos Erres massacre.

During a phone interview from a Canadian jail last year with ProPublica, Sosa insisted he was not present at Dos Erres on the day of the crime. During the interview and in letters provided to ProPublica by his brother, Sosa claimed that he was working 100 miles away on a civil affairs project in a town called Melchor de Mencos, where he said he helped residents obtain school and sports supplies.

The defense has not repeated that claim during the trial. Without explicitly admitting Sosa’s involvement, Kewalramani’s opening argument emphasized the idea that the Guatemalan civil war was a brutal conflict and that Sosa was part of an elite unit that was trained to carry out orders. Sosa will not testify, his lawyer said Friday.

The prosecution ended its case with testimony from Ramiro Osorio Cristales. Osorio is the eldest of two boys who were spared, abducted by commandos and brought up in the soldiers’ families. The other boy, Oscar Ramírez Castañeda, was only three and does not remember anything about Dos Erres. Ramírez now lives in Boston and his story was told by ProPublica last year.

Osorio lives in Canada. He was 5 years old when he lost his parents and six siblings in the massacre. He described his memories in accented but clear English, his voice breaking, pausing to regain his composure.

Osorio recalled that armed men burst into his house at night and dragged out the family. The men tied up his father and older brother with ropes around their hands and necks and brought them to the school with the rest of the men of the hamlet, he testified. The assailants herded the other children and their mother into the church with the terrified women and children of Dos Erres, according to his testimony.

“They started taking out women from the church,” Osorio testified. “They grabbed a woman by her hair and pulled her out, some young girls, teenagers. Their mom was saying ‘Please don’t take my kids.’”

Osorio watched between the wooden slats of the church walls as soldiers raped women and killed children by smashing them against a tree, according to his testimony.

“They treated them like animals,” he said.

Then the soldiers came for Osorio’s mother, he testified.

“I remember grabbing my mom by her leg,” he testified. “We was fighting with the guys … ‘Don’t take my mom.’ I ran to the back of the church to see what was happening to my mom. She was screaming for help: ‘Please don’t kill us. Don’t kill us. Don’t kill my kids, they don’t know nothing.’ ”

Osorio said he eventually fell asleep under a bench in the church. When he awoke, he testified, only four other children remained. Three of them were girls whom the commandos raped and murdered the next day. Only Osorio and Ramírez survived.  When Osorio finished his testimony, jurors and spectators wiped away tears.

The trial is likely to end Monday because the prosecution pared down its initial list of witnesses, choosing not to call two more former commandos. The judge also said she has tried to speed up the trial because of the imminent possibility of a shutdown of the federal government. If the defense decides to call the former prosecutor who has questioned Franco’s truthfulness, that testimony will take place Monday before closing arguments.

Clarification: This story has been revised to clarify Osorio’s testimony that he was one of five children still alive after the soldiers’ initial assault on Dos Erres.