BROOKLINE — A man was arrested Wednesday at a home in Malden on a warrant charging him with the fatal stabbing of a 20-year-old man at Amory Playground early Tuesday morning, the authorities said.
Singha Oeun, 21, of Brookline, charged with murder in the slaying of Nicolas “Cole” Kern, was set to be arraigned at 9 a.m. Thursday in Brookline District Court.
Norfolk District Attorney Michael Morrissey said Oeun was arrested after state, Brookline, and Malden police executed a warrant to enter a residence on Wallace Circle in Malden. Morrissey said Kern and Oeun knew each other but declined to detail the nature of the relationship.
Nor would he comment on motives, the weapon used, or the home where Oeun was arrested at about 12:30 p.m.
“You’ll learn more tomorrow” at the arraignment, Morrissey said at a press conference at the Brookline police station.
Brookline Police Chief Andrew Lipson said there was no danger to the public. “This was an isolated incident,” he said.
Kern’s death is Brookline’s first homicide since 2006.
Officers responded to the park after a report of an assault and battery with a dangerous weapon at 1:38 a.m., Lieutenant Philip Harrington of the Brookline police had said earlier Wednesday. The victim was taken to Beth Israel Deaconess Medical Center in serious condition, he said.
The man died “following extensive medical treatment,” according to the district attorney’s office.
The public’s help was crucial, Lipson said. “Cooperation from members of the community and a trail of technological evidence were essential in this case,” he said.
Kern, of Brookline, was a 2018 graduate of Cushing Academy in Ashburnam, Head of School Randy R. Bertin said. “Our community is deeply saddened by the loss and keeping his family in our thoughts,” Bertin added.
Attempts to reach the Kern family were unsuccessful Wednesday.
Oeun lived at 55 Egmont St., an apartment building that appears to be part of a larger Brookline Housing Authority complex.
Officials at the public housing authority could not immediately be reached for comment Wednesday night, and no one answered Oeun’s apartment buzzer.
Residents of the three-story brick apartment complex said it is usually quiet. But the peace was broken Tuesday when police swarmed the complex for several hours.
“I’ve never seen anything like it,” said Mercedes Sanchez, 64, who has lived in the complex for 15 years.
Aracelis Sanchez, 36, described the neighborhood as “always calm.”
“I have two kids,” she said. “It’s scary” what happened.
A 28-year-old who works in construction management said that she would see Oeun while walking her two dogs. The woman, who declined to be named, said that she would say “Hi” to Oeun but did not know him beyond that.
She said police were questioning neighbors Tuesday and that they appeared to be waiting for Oeun at the apartment.
“I think everyone is in shock,” she said.
The apartment complex is a short distance from Amory Playground, a popular eight-acre spot that has ball fields, walking paths, and other amenities. The park was quiet Wednesday evening. A cold, steady rain fell, pooling water on the infield of one of the baseball diamonds.
Brookline resident Johanna Selvaggi, 51,frequents the park. Pausing from calling after her dog, a hound named Shek who had run onto the fields, she said that some people in the community wish the park was better lit at night.
“The community is shocked about this,” said Selvaggi, who said she would like to see lights installed. “This, like, 20-year-old kid . . . it could be any of our kids.”
Another resident said that she was shocked to learn that someone had been stabbed in the park. The neighborhood is usually safe and quiet, she said.
“People joke that nothing ever happens in Brookline,” said the woman, who asked that her name not be published. “It’s scary.”
Wallace Circle, the cul-de-sac in a thickly residential Malden neighborhood where Oeun was arrested, was also quiet Wednesday evening.
Nadia Farah, 40, a scientist who lives there, was not home for the arrest, but found it unnerving. “I don’t like it,” she said. “I’m very uncomfortable.”
Correspondent Sofia Saris and Travis Andersen of the Globe staff contributed. Sweeney can be reached at esweeney @globe.com, Follow her on Twitter @emilysweeney.McDonald at email@example.com. Follow him on Twitter @danny_mcdonald.