A former Dorchester resident pleaded guilty Wednesday in the May 2011 shooting death of 19-year-old Derek Matulina at the Savin Hill Red Line station. Nhu Nguyen, 20, was sentenced to two and a half years in jail in a plea deal. He'll be on probation for two additional years, according to Suffolk County District Attorney Daniel F. Conley's office.

Nguyen shot Matulina in the chest during a fight on the T station platform on the afternoon of May 7. Prosecutors said Nguyen and Matulina "had once been friends and had sold marijuana together but had had a falling out over the proceeds of those sales."

The two men crossed paths by chance at the T station that day, Conley's office reports.

"Nguyen demanded money that he felt was owed him and Matulina responded by challenging him to a fight. At that point, Nguyen produced the .22 caliber handgun he had been carrying, and others separated the two," the DA's office said.

Matulina followed Nguyen and assaulted him from behind, striking him repeatedly in the head with a padlock wrapped in a bandanna. Nguyen shot Matulina once in the chest, killing him.