An argument Tuesday at a Riverhead apartment complex ended with a young woman stabbing her boyfriend to death, Suffolk police said.

Police responded to a call of a domestic disturbance on East Main Street at the home of Kianna Coach, 21, at 11:40 a.m. When they arrived officers discovered Coach's boyfriend, James Wheeler, 25, of Riverhead, lying on the lawn outside the apartment complex. He had been stabbed in the chest.

Wheeler was taken to Peconic Bay Medical Center in Riverhead, where he died 45 minutes later, said Suffolk Det. Lt. Jack Fitzpatrick, commander of the homicide squad.

"There was an argument that escalated when Miss Coach retrieved a knife and stabbed Mr. Wheeler in the chest," Fitzpatrick said. "He then fled the apartment and collapsed on the lawn outside the complex."

Coach was arrested in her apartment and charged with first-degree manslaughter. After being taken into custody, she passed out and received medical attention. Police did not elaborate on her whereabouts. She will be arraigned at Riverhead Justice Court Wednesday morning, police said.

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Asked why Coach had been charged with manslaughter instead of murder, a higher charge, Fitzpatrick said, "It's not uncommon to charge manslaughter in this particular case." He did not provide details. "The district attorney would have the option to put it in front of a grand jury and determine if they want to upgrade the charges."

Fitzpatrick he said he did not know what the argument was about or how long the couple had been together.

"There's no known domestic issues between them," Fitzpatrick said.

Relatives from either family could not be reached. Neighbors of Coach reached by phone declined to comment.