Kevin Rivera and Amber Diaz started arguing after their daughter 's party . Miss Diaz 's grandfather , Nicolas Diaz , 81 , allegedly intervened with knife . He 'stabbed Mr Rivera in the chest ' ; fled the scene after Sunday 's killing . Victim rushed to hospital with stab wound , where he was declared dead . Diaz turned himself in to police in New York , Brooklyn , Monday morning . Has been charged with manslaughter , while baby girl is now in custody .
Kevin Rivera and Amber Diaz started arguing after their daughter 's party . Miss Diaz 's grandfather , Nicolas Diaz , 81 , allegedly intervened with knife . He 'stabbed Mr Rivera in the chest ' ; fled the scene after Sunday 's killing . Victim rushed to hospital with stab wound , where he was declared dead . Diaz turned himself in to police in Brooklyn , New York , Monday morning . Has been charged with manslaughter , while baby girl is now in custody .