A Dorchester teen was formally charged today with ending a May 7 physical confrontation with a bullet to his opponent’s chest, Suffolk County District Attorney Daniel F. Conley said.

NHU NGUYEN (D.O.B. 5/5/92) is charged with a single count of murder for the shooting death of 19-year-old Derek Matulina at an MBTA Red Line station. Dorchester District Court Judge James Coffey ordered Nguyen held without bail and ordered him to return to court on June 21.

Assistant District Attorney Holly Broadbent told the court that the two young men were known to each other prior to the afternoon incident at Savin Hill station. Tension had escalated between the two in the weeks leading up to May 7, she said.

Shortly before 3:00, Broadbent said, Nguyen and Matulina became embroiled in an argument outside the station that continued onto the platform. There, Matulina approached Nguyen from behind and struck him several times with a padlock wrapped inside a bandanna.

A third individual at the scene separated the two men, Broadbent said. It was then that Nguyen allegedly stepped back, gestured to his waist, pulled a gun, and fired a single shot that struck Matulina in the torso.

Matulina ran a short distance and called 911 before collapsing, Broadbent said. Boston Police and MBTA Transit Police arrived a short time later and launched an investigation that led to the recovery of surveillance images and a series of witness statements.

Prosecutors approved a warrant for Nguyen’s arrest on May 10. Boston Police assigned to the Fugitive and Apprehension Unit located Nguyen at the Portland, Maine, home of an acquaintance on May 10. He waived rendition proceedings and was returned to Boston yesterday. The investigation by Boston Police, Transit Police, and Suffolk prosecutors is ongoing.

Kara Hayes is the DA’s assigned victim-witness advocate. The defendant is represented by attorney Randy Gioia.