ProPublica's Sebastian Roella and Fundación's Ana Arana report:

Chapter 1: 'You Don't Know Me'

The call from Guatemala put Oscar on edge.

Prosecutors came looking for you, relatives in his rural hometown told him. Big shots from Guatemala City. They want to talk to you.

Oscar Alfredo Ramírez Castañeda had plenty to lose. Although he was living in the United States illegally, the 31-year-old had built a solid life. He worked two full-time jobs to support his three children and their mother, Nidia. They had settled in a small but cheerful townhouse in Framingham, Mass., a blue-collar suburb of Boston.

Oscar usually did his best to avoid contact with the authorities. But he decided to call the prosecutor in Guatemala City. She said it was a sensitive matter about his childhood and a massacre in the country's civil war long ago. She promised to explain in an email.

Days later, Oscar sat at his computer in a living room full of toys, school trophies, family photos, a crucifix and souvenirs of his native land. He had arrived home from work late at night, as usual. Nidia, seven months pregnant, rested on a couch nearby. The children slept upstairs.

Oscar's green eyes scanned the screen. The email had arrived. He took a breath and clicked.

"You don't know me," it began.

Prosecutor Sara Romero's Letter to Oscar