They were first cousins, close friends since childhood. But after a night of drinking, police said, a discussion turned into an argument, then a fistfight and then a killing when one slammed the other “head first into the pavement of the street.”

On Friday, D.C. police said a fugitive squad arrested the man who had been sought in the fatal beating since shortly after it occurred May 26 at Abbey Place and L Street NE, about five blocks from where the victim lived with his grandmother. Arvel Wills, 23, of Northwest Washington is charged with second-degree murder in the death of Dwayne Wills, 25.

Court documents and interviews with family members offer few details of what might have caused the dispute to turn deadly.

“I don’t know what happened,” said the victim’s sister, Andrea Wills, 26. “I heard they were arguing and started fighting.”

She said her brother had a 4-year-old daughter and was trying to get his high school equivalency degree. “He was trying to better his soul,” she said.

Documents filed Friday in D.C. Superior Court say the cousins were outside drinking about 4 a.m. after returning from a club. During a heated exchange, police said, Arvel Wills threw two punches at his cousin.

According to the charging document, Arvel Wills picked up his cousin, held him above his head and threw him to the ground. Dwayne Wills fell unconscious but then came to and asked for help. Police said relatives drove him to Washington Hospital Center.

He told a doctor at the hospital that he “got dizzy and fell,” according to the court papers.

Authorities said he went into a coma May 29 and died June 4. His death was ruled a homicide by blunt-force trauma.

Court records show that Arvel Wills has had previous encounters with police, including convictions for destruction of property in 2007 and assault in 2008.

Dwayne Wills was convicted of assaulting a D.C. police officer in November 2009, according to court records, after he got drunk and refused to leave his grandmother’s house.

Lorraine Wills, Dwayne’s 78-year-old grandmother, said she had raised him since he was 9 after his mother died of a brain aneurism. “He wasn’t a bad boy,” she said.

She said the cousins played together as children and hung out together as adults. She, too, said she had no idea what could have prompted the attack that led to his death.