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.

The killing of the sunny-faced boy instantly earned that grim distinction of “every parent’s worst nightmare.” And it arrived at a particularly uneasy moment in New York City, when violent crime is statistically down, yet the opposite can feel true on the streets.

The issues of mental illness and recidivism resurface regularly as high-profile killings and attacks dominate news cycles. Gov. Kathy Hochul and candidates in the city’s mayoral race each have versions of plans to prevent random attacks, including by allowing hospitals to commit more people whose mental illness have put them or others at risk.

“The systems that we have in place to deal with repeat offenders and individuals with severe mental health issues continue to fail us,” said Jessica Tisch, the police commissioner, after Mr. Mejia’s arrest. “My message to New Yorkers is: ‘Something has to give.’”

Born in 1995, Mr. Mejia was a quiet and curious child, said his friend, Mr. Beato. “Very on point with things at school,” he said. The two remained close through high school and beyond. Mr. Beato sells cars at a Honda dealership, and describes experiencing a true kinship with Mr. Mejia, even as he sometimes felt like a big brother, keeping the other man on the right path.

When Mr. Mejia would veer into bizarre territory in their conversations, Mr. Beato said, “I would tell him, ‘Hey, my brother, that’s not correct.’”

Mr. Mejia’s parents split, and his father, a dentist, moved to California. He lived with his mother in the Kingsbridge neighborhood of the Bronx for most of his 20s, and bore her name, Lucia, on his tattooed torso. He was an avid boxing fan through high school.

He had been arrested as a teen for minor offenses like marijuana or alcohol possession, but his first serious charges came in 2017, when he was 21. He’d called his mother at work and told her he was going to break everything in their home, she told the police. She arrived to find he was well along — her flat-screen television was smashed and a sofa was overturned. When she made to leave, he told her he had a gun, and she called the police.

Officers found a loaded pistol under sofa cushions. Mr. Mejia said he had bought it for protection, according to court records. He was charged with possession of a weapon and pleaded guilty, and when he completed mandated mental health treatment, the conviction was dismissed.

Two years later, when he was 23, Mr. Mejia was showing psychic cracks that alarmed his old friend, Mr. Beato. He told others he wanted to be called “Anthony Luciano,” and he set about having his name legally changed. His childhood curiosity — “very philosophical, always thinking, always trying to find the ‘why’ of stuff,” Mr. Beato said — had morphed into fixations and dark rabbit holes.

“His girlfriend at the time, her mother had some cahoots with Floyd Mayweather,” the former boxing champion, Mr. Beato said. “He gained a weird obsession with that.”

Voices followed, warning him about the girlfriend.

“The voices in his head were Floyd Mayweather and Jadakiss, the rapper,” Mr. Beato said. “I think the voices in his head were telling him she was after him — the Floyd Mayweather, Jadakiss voices.”

On April 7, 2019, Mr. Mejia arrived at his girlfriend’s apartment building on Bailey Avenue, splashed a flammable liquid on the floor of the vestibule and lit it on fire. No one was hurt, the damage was minimal and Mr. Mejia, who was seen on video setting the fire, was quickly arrested and charged with arson.

He was allowed to plead guilty to a lesser charge, reckless endangerment, on the condition that he undergo mental health treatment, which he did.

He told his friend he had been diagnosed with schizophrenia and was taking strong medication.

“The meds used to make him feel weird,” Mr. Beato said. “He wasn’t too fond. I used to remind him here or there” to take the medicine. It seemed to be working. “He’s so monotone and chill. I’m thinking that’s when he was on the medication.”

When Mr. Beato saw him about six months ago, his friend was upbeat, working as a delivery driver and thinking about the future. They spoke less frequently in the months that followed, but that was not unusual, both men busy.

Then Mr. Beato saw a selfie of his friend on Instagram that gave him pause.

“His eyes looked sunken in, he was losing weight,” Mr. Beato said. “He looked like he was getting skinny in the face, signs that people aren’t eating or getting sleep.”

By then, he said, Mr. Mejia was apparently living alone in an apartment in Mott Haven in his father’s name, a tidy fourth-floor walkup on Alexander Avenue. There, on Nov. 27, something set him off.

He’d been banging on neighbors’ doors, and one of them watched on a Ring doorbell camera mounted outside his second-floor apartment. The man opened his door and told Mr. Mejia, who he only knew in passing, to cut it out.

Mr. Mejia went upstairs to his apartment and returned with a knife. Stone-faced, he stabbed the neighbor’s Ring camera over and over until its lens shattered.

The footage of the act was striking, so calmly intent was Mr. Mejia in his bizarre task. Weeks later it would lead to second-guessing: How could this man have been allowed to walk the streets?

But attacking the camera did not appear to set off major alarms about Mr. Mejia, whose last conviction, for setting the vestibule fire, had been more than five years earlier. He was charged with criminal mischief and harassment, both misdemeanors that do not qualify for immediate jail time. He was released on his own recognizance.

Weeks later, shortly after midnight on Jan. 5, Mr. Beato got a text from his friend without any context: “Remember those days me going in your closet for snacks and fridge,” it began. “Imagine that being people possessing my body to do those things.”

Then, some three hours later, according to the police, Mr. Mejia entered the subway station outside his apartment on East 138th Street and stabbed a stranger through his left arm, piercing his chest. The knife struck an artery in the victim’s arm, and he lost consciousness as he bled, but survived after surgery, according to a criminal complaint.

Investigators did not immediately identify the stabber, who was caught on cameras.

Two days later, Mr. Beato got another random text, this time a picture of a moldy shower. “Is it similar,” Mr. Mejia asked, adding that it was “safe to respond.”

“Similar to what,” Mr. Beato replied, and the conversation ended.

On the other side of East 138th Street, in a tall public housing building in far greater disrepair than Mr. Mejia’s walkup — the lobby ceiling leaks water near the mailboxes — Caleb Rijos, 14, lived with his father and sister on the 14th floor.

He wanted to move; when he was visiting his aunt in Middletown, in the Hudson Valley, in December, he had told her that he would love to live there.

But he was also happy in his life in the Bronx.

“He would say, ‘Hey Daddy, let’s watch TV. What do you want to do today?’” said the aunt, Amarilis Rijos.

He’d been a quiet middle-schooler who seemed to open up after graduating eighth grade. At Bronx Leadership Academy High School, he was both a focused student and a lot of fun.

“He was the nicest boy,” said a friend, Heidi Escalera, 14. “Whenever someone had a beef or a drama, he’d always check up on him. He was never sad. He was so goofy.”

Caleb left his apartment on Jan. 10 to head to school, and walked to a bus stop and straight into the path of a troubled man with a knife. Stabbed and bleeding, he ran to East 138th Street, pulled out his phone and called his father.

Hello? his father, Jacob Rijos, said. Hello? No response. Just a gasping sound, “like someone is choking with blood,” Caleb’s aunt, Ms. Rijos, said her brother told her. The line went dead.

Mr. Rijos used the Find My Phone feature, and saw his son was on East 138th. He headed for the building’s slow, overworked elevators to make his way down. By then, the boy had fallen between two parked cars, and strangers had flagged down a passing ambulance.

When Mr. Rijos arrived where the phone had been, it, and Caleb, were gone. He tracked the phone again. Now it was at Lincoln Hospital. He rushed there himself, where doctors told him the unthinkable. Caleb was dead.

“It’s hard right now,” he said in an interview that day, shellshocked. “We still don’t know what happened.”

The police were learning more. A photo of the suspect in Caleb’s death, taken from nearby cameras, was pushed out to every officer, and one realized it was the same man as the one seen in the footage of the nearby subway stabbing five days earlier.

Officers searched for other crimes involving a knife in the area, and found the Ring camera case. They quickly matched the man in the surveillance videos with the defendant in the camera stabbing: Waldo Mejia.

Officers waited for him at his apartment on Alexander Avenue, where he was arrested the following morning. He was carrying a bloody knife, the police said.

His friend, Mr. Beato, was at work when a cousin called with the news. “I just felt like a blank. Like a silent sheet just wrapped over me and all I heard was white noise. You know, when the hairs stand up on your body. How? How can that happen? I was very angry.”

At a court appearance the next day, Mr. Mejia shouted, “I’m with Satan!” according to the New York Daily News. He remains in custody, charged with Caleb’s murder as well as in the Jan. 5 subway stabbing.

Caleb’s death shook his community and prompted at least three memorials, vigils and marches in the week that followed. On Friday evening, friends, family and strangers released balloons into the darkening sky. Caleb’s family stood in a tight huddle, warding off reporters.

“They’re wearing the trauma,” said Shaya Been, 32, with the anti-gun group Save Our Streets, which turned out for the Friday event. “We lost a child. We don’t normalize that kind of thing around here.”

Mr. Mejia’s friend Mr. Beato is among those who think the stabbing of the Ring camera should somehow have been taken more seriously.

“If I see somebody with a history of schizophrenia and he’s using a knife, I wouldn’t release him into society,” he said. “He’s mentally not there. He thought about it. He thought: ‘This is a good idea, to stab this.’”

Kitty Bennett contributed research.