The Voices in His Head Would Not Stop. Then a Boy Was Stabbed to Death.

Waldo Mejia, living in the Bronx, was in his early 20s when he told one of his oldest friends about the voices in his head. He seemed surprised at what they were ordering, and moreover, at how he so readily obeyed.

“It was something telling him these things,” said the friend, Mozart Beato, 29, who has known Mr. Mejia since third grade. He told wild stories about what happened next, with details that were scant and obscure.

“One time, the voices in his head sent him to Mississippi on a Greyhound — he actually did that,” Mr. Beato said. “He went on that side mission. Found himself in a warehouse surrounded by a whole bunch of random people. He was like, ‘Oh man, I was bugging out.’ He was conscious of the fact that that was pretty crazy to do.”

The voices would change, and with medication, go quiet for stretches. But it seems they never went away.

On Jan. 10, a cold Friday morning, a 14-year-old boy, Caleb Rijos, was walking to school in the Mott Haven section of the Bronx when a stranger approached and stabbed him twice in the chest, piercing his heart and lung and killing him. That stranger, the police said, was Mr. Mejia, who was quickly arrested.

Later that day, he would shout out in court that he was “with Satan,” a chilling reminder of the voices he had told his friend about.