A troubled man, a straight-A student and a fatal stabbing that shocked L.A.

Something seemed deeply wrong with David Zapata.

Claudia Montes, his ex-girlfriend and the mother of his child, knew it. So did his friends, who sent her Facebook messages expressing their concern.

Zapata had stopped responding to calls. He wouldn’t answer when Montes asked him questions. Sometimes he thought she’d said something when she hadn’t opened her mouth at all. She said he believed he’d solved the 2008 killing of her brother — whom he’d never met. And he would speak about himself in the first person plural.

Images were released of the suspect in two stabbings in Los Angeles on March 3.

(Los Angeles Police Department)

“We know what you’re doing,” he would say to Montes, speaking only for himself, she said.

“For a long time I would say … ‘Something is wrong with David. He doesn’t seem right,’ ” Montes said.

Police say that disturbing behavior culminated Friday, when a 17-year-old honors student was stabbed to death outside a King Torta on Valley Boulevard in El Sereno while waiting for his family to pick him up after school. Hours later, a 33-year-old man was stabbed repeatedly on the same street, authorities said.

Surveillance video shows the moments just before the fatal stabbing of Xavier Chavarin, when the assailant walked up behind the teen brandishing a long blade. Montes said the man in the video was her ex-boyfriend.

Zapata, 32, was arrested Wednesday on suspicion of murder in Xavier’s death after barricading himself inside his home in Alhambra for several hours during a standoff with Los Angeles police. Officials say Zapata also stabbed the second man, who survived his injuries. Bail was set at $2 million.

Xavier’s killing has left his classmates at Woodrow Wilson High School reeling, with counselors available to help those grieving.

“I have a senior class and most of them were affected,” said Alan Chau, a social studies teacher who knew Xavier for three years. “We just sat there all day Monday and had discussions about it.”

The boy was a model student, said Chau, who taught him U.S. history and also was his homeroom teacher.

“In general, Xavier is just an easygoing kid, very open. He went with the flow,” his teacher said. “He is loyal to his friends at school. … He asked questions. He doesn’t talk back. He’s a hardworking kid in the classroom.”

Xavier loved to draw, and Chau said he had expressed a desire to become a graphic designer, adding the high school senior had set his sights on Los Angeles Trade–Technical College.

“It breaks my heart the fact that they just took him away from me,” Laura Frias, Xavier’s mother, said in an interview with NBC4.

The family went to the funeral home Wednesday to make final arrangements for her son’s burial.

Authorities surround a residence in Alhambra where they believe a suspect who fatally stabbed a 17-year-old boy and injured a man in Los Angeles was barricaded.

(Irfan Khan / Los Angeles Times)

Hours before that, Los Angeles police detectives arrived at a house in the 2300 block of Westmont Drive in Alhambra after receiving a tip that the man who lived there was the same person seen in video of the knife-wielding attacker, Cmdr. German Hurtado said. LAPD gang and narcotics division officers surrounded the home around 7 a.m., and a Special Weapons and Tactics team brought in two armored vehicles and blocked the surrounding area.

Hurtado said a crisis negotiator was able to persuade Zapata, who was in the home alone, that he would be safe to walk out. The crisis negotiator and a mental health evaluation team, along with the man’s mother, talked to him on his cellphone for hours before he surrendered, Hurtado said.

The family of the boy police said Zapata killed anxiously waited outside during the standoff. Frias, his mother, broke down when Zapata’s surrender was announced. Her father, Jesus Frias, comforted her as she hid her face and openly wept.

Daniel Chavarin, the teen’s father, wanted to see the person accused of killing his son get taken away by police.

“It didn’t bring me any kind of relief, but it was … it was to be certain that they got him,” Chavarin said.

Daniel Chavarin, left, father of 17-year-old Xavier Chavarin, who was fatally stabbed last week in El Sereno, talks with police officers at the location where the stabbing suspect barricaded himself in Alhambra.

(Irfan Khan / Los Angeles Times)

Although a motive in Xavier’s slaying remains unclear, Councilman Kevin de León — whose district includes the site of the attack — said Wednesday that the streets of Los Angeles “are the largest psychiatric ward in the United States.”

“Unfortunately, it has become quite normalized in Los Angeles for someone to walk up to someone and snap … or just hit someone,” said De León, who waited outside Zapata’s home with Xavier’s family.

“There’s no question about it; he’s suffered from severe mental illness,” he said of the stabbing suspect.

Jorja Leap, a professor in the Social Welfare Department at the UCLA Luskin School of Public Affairs, refuted De León’s comments, saying it was “inaccurate and irresponsible” to paint L.A. with such a broad brush depicting mental illness.

The Los Angeles Police Department and other law enforcement agencies do not track crimes committed by mentally ill people, Leap said.

“So many [people with mental health issues] cannot even care for themselves, let alone think about taking the life of another human being,” she said.

It was not immediately clear whether Zapata had ever been diagnosed with mental health problems, yet Montes and others said he was clearly unwell.

A woman who works at Valley Food Liquor on the block where the second stabbing occurred remembered a strange customer who would buy beer and cigars but would not speak, even when she greeted him and tried to spark conversation.

The taciturn description matched how Montes said Zapata had behaved in recent years.

The man she dated was friendly, comfortable and talkative, she said, but lately, he had become withdrawn.

“He wouldn’t seem like he was there. He would be quiet,” Montes said.

The two dated from 2008 to 2012, but Montes said she broke up with Zapata because of his methamphetamine habit, which she said kept him awake all night. They had been in a band called Narfarus, and Zapata was an extremely talented drummer who toured with other groups, Montes said.

Court records show Zapata had minor run-ins with the law before this week.

He was convicted in 2013 of driving a vehicle without a license and got a year’s probation. In 2017, he was charged with driving on a revoked license, but prosecutors dismissed the case. In September 2020, he was convicted of misdemeanor hit-and-run and driving with a blood alcohol level above the state limit. He spent two days in jail and was placed on probation for three years.

Montes has custody of her and Zapata’s teenage son. She said that she had not been in contact with Zapata for some time, but that in the last two weeks he began texting and calling their son. He seemed paranoid, Montes said.

Still, she said, she had never known Zapata to be violent. “I never saw a side like that of him.”