Jashaya Stanley, 19, of Brooklyn had gotten into a brawl with ex-con Joshua Knox just moments before he allegedly opened fire on the mother of his 3-year-old daughter, the New York Daily News reported.
Family members and witnesses told the Daily News Stanley had splashed bleach on Knox after he punched her in the face during an argument.
"He shot her six times in the chest," said Deridre Baker, Stanley's aunt. "He couldn't beat her. I guess he had to kill her."
Police were searching for Knox who fled after the shooting Monday evening.
He was released earlier this month after being imprisoned on drug selling charges.
Stanley appeared in March on Nancy Grace's "Swift Justice" TV show.