But within hours of learning that skill, prosecutors say Martins, who turned 18 last week, was stabbed and killed during a fight at a city park in the neighborhood where the famed boxer Rocky Marciano grew up. Two others were injured, but are expected to survive, prosecutors said.

“He said, ‘I can save your life if [you are in danger],’ ’’ said his guardian Janish Rojas. “He was so happy he learned to save a life.”

BROCKTON — Ywron Martins came home from his CPR class Wednesday and proudly talked about what he had just learned.

On Thursday evening, Rojas returned to the spot in James Edgar Playground where the teen who called her Ma had collapsed, bleeding. She pleaded with mourners to help police solve the crime.


“I know a lot of you saw what happened. Please say something,” Rojas, 37, told a crowd of young people who gathered to light candles and leave flowers. “I don’t want his death to be in vain. This could have been any of you guys. None of you deserve to lose your life.”

Just before the vigil, investigators announced an arrest warrant had been issued charging Anildo Lopes Correia, 24, in the slaying, according to the office of Plymouth District Attorney Timothy J. Cruz.

Prosecutors said there was no reason to believe Correia, who also goes by the name “Ace,” posed a specific threat to any individual or the community, but given his suspected involvement in the stabbing, the public was asked not to approach him, but instead contact authorities.

Rojas said Martins and Correia were friends at one point, but that Martins had recently started distancing himself from some of his associates.

“He started separating himself from certain people,” she said. After returning home from CPR class, Rojas said, Martins took a nap. She woke him up, she said, after he started getting calls inviting him to play basketball at the park.


Anildo Lopes Correia. Courtesy Plymouth County District Attorney’s office

At first, Rojas said, Martins was not interested in going out, but then changed his mind and left for the park.

“I was like, ‘Be careful and don’t be naughty,’ ” she said.

When she learned of the stabbing, Rojas said she ran to the park, but Martins had been taken to Good Samaritan Medical Center in Brockton.

“I didn’t make it in time,” Rojas said. “He died in the operating room.”

Martins suffered stab wounds to his stomach, heart, and neck, said his cousin Romaldo Lopes, 17.

“Someone stabbed him in his heart, where he loved us,” said Rojas’s 11-year-old daughter Leyla.

Rojas said she met Martins after he became friends with her daughter, Jhakaila, 14, and became his guardian with the blessing of Martins’ father, who also lives in Brockton.

Martins turned 18 on April 15 and officially became an adult, but continued to live with Rojas, she said. Martins’ mother lives in Cape Verde, and his father was vacationing there when the stabbing happened, Rojas said.

Martins had been in trouble with the law and was recently enrolled in a program that was helping him find work, Rojas said. He had taken steps to re-enroll in school and was scheduled to have a meeting about his job search Thursday, she said.

“That’s my son,” Rojas said. “His life was worth so much.”

The fatal stabbing struck a nerve in the city, which had invested about $750,000 in recent improvements to the park, said Mayor Bill Carpenter. The park was reopened and rededicated last year, he said. It includes a playground, skatepark, baseball and soccer fields, and volleyball court. But some residents complained the police presence there is inadequate.


“At night, you have between 4 and 9 p.m., you have approximately 300 people here of all different nationalities having a great time,” said Dennis Hursey, who visited the park Thursday morning. “For some reason, there is not an officer stationed here. That, to me, is horrible.”

Teens hug on James Edgar Playground in Brockton. Rose Lincoln for the Boston Globe/Globe Freelance

Hursey said police could have prevented the violence.

“If we had a police officer here, this would have never, ever happened,” he said.

But Carpenter said at a City Hall news conference Thursday afternoon that there was a robust police presence at the park and Brockton motorcycle patrol officers had just left when the fight erupted around 6:42 p.m. Wednesday.

He said state troopers who work with the city’s gang unit came upon the fight while it was happening and intervened.

“Police presence or lack thereof was not a factor in any way. Quite the opposite,” Carpenter said.

Carpenter described the incident as “isolated,” but said surveillance cameras will be installed at the park and more patrols will be assigned there, including police on motorcycles, more cruisers, and an officer on a walking beat.

He also announced that a neighborhood block party at the park was planned for May 17. “The parks and playgrounds belong to families and children. They do not belong to thugs and criminals,” Carpenter said. He said about 100 people were at the park when the fight broke out.


“This is the playground, the ballfield that Rocky Marciano grew up on,” he said. “When Rocky got hit in the mouth, he hit it back. And that’s exactly what we’re going to do.”

John R. Ellement contributed to this report. Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi.