A Revere youth yesterday admitted to beating Robert Mackey with a golf club, causing injuries that went untreated and took the 58-year-old Winthrop man’s life a week later, Suffolk County District Attorney Daniel F. Conley said today.

MATTHEW RILEY (D.O.B. 7/12/89) pleaded guilty to manslaughter in connection with the Aug. 12, 2007, incident outside a Winthrop convenience store. Riley also pleaded guilty to two counts of assault and battery with a dangerous weapon – for striking Mackey and another adult male – and possession of a Class D substance with intent to distribute.

Suffolk Superior Court Judge Christine McEvoy sentenced Riley to a term of five to seven years in state prison, the term recommended by Assistant District Attorney Mark Zanini, and 10 years of probation upon his release.

Present for the proceedings were the victim’s brothers, wife, and daughter, who delivered impact statements describing to the court the loss they suffered when Mackey died of his injuries.

Riley, tearful throughout the proceedings, addressed them directly afterwards, expressing remorse for his actions and their repercussions.

Had the case proceeded to trial, prosecutors would have shown that Riley and his brother were involved in a dispute with the victim and another man outside a Revere Street convenience store shortly after 2:30 a.m. That dispute escalated to a violent physical altercation among Riley, Mackey, and their respective associates.

Prosecutors would have demonstrated that Riley repeatedly hit Mackey in the lower left back with the golf club in the course of the altercation, causing severe blunt trauma to the man’s left posterior ribcage. Riley was transported to an area hospital in the aftermath of the incident but left without receiving medical treatment. Meanwhile, responding Winthrop police discovered a quantity of marijuana in Riley’s car.

Mackey returned to the hospital several days later, not knowing that he had suffered a lacerated spleen. He underwent surgery but passed away a short time later.

Riley was initially charged only with assault and battery with a dangerous weapon. The manslaughter indictment was returned on March 3, 2008, after a Suffolk County grand jury considered Mackey’s death among the facts and circumstances of the incident.

Conley called it an “extremely sad” case for two families.

“But as sad as it is for the Riley family to see this young man walked off to state prison, it is exponentially worse for the Mackey family, who will never again get to see him, speak with him, hug him, or tell him they love him,” Conley said.

Riley was represented by attorney Thomas Brandt.