Suffolk County District Attorney Daniel F. Conley today announced upgraded charges against a Roslindale man charged with killing 23-year-old Andrew Prior in a collision on Tremont Street last year.

The Suffolk County Grand Jury on June 27 returned indictments charging COLIN RATIU (D.O.B. 11/27/87) with motor vehicle homicide while operating under the influence of alcohol and leaving the scene of an accident causing death. Ratiu is expected to be arraigned on those charges in the Magistrate’s Session of Suffolk Superior Court at 2:00 tomorrow afternoon.

The lead indictment supersedes a West Roxbury District Court complaint charging Ratiu with motor vehicle homicide by negligent operation. Ratiu was arraigned on that charge on Feb. 14 and was released on $7,500. The next day, he was arrested again on drug charges after Boston Police executed a search warrant on his home and discovered a climate-controlled grow room stocked with four large marijuana plants.

Massachusetts law provides for up to 15 years in state prison and a fine of up to $5,000 for motor vehicle homicide while operating under the influence. Negligent motor vehicle homicide carries a maximum of two and a half years in a house of correction. Leaving the scene of an accident causing death is punishable by up to 10 years in prison.

Prosecutors say Ratiu was driving a blue Hyndai Santa Fe sport-utility vehicle drunk and at a high rate of speed on the night of Nov. 14, 2010, when he collided with Prior, who was travelling on his scooter. Ratiu allegedly continued driving toward Brigham Circle without stopping.

Boston Police responded to the scene shortly before 11:30 p.m. to find Prior, a Syracuse man attending school in Boston, suffering from fatal injuries. He was rushed to Brigham and Women’s Hospital, where he was pronounced dead.

Shortly after the collision, Boston Police publicized the make and model of the suspect vehicle and asked area auto body shops to be mindful of such vehicles needing repairs for unexplained damage.

Acting on information developed during the investigation, Boston Police homicide detectives in February found the Santa Fe parked near Ratiu’s home. The vehicle had sustained significant front end and windshield damage and both its airbags had been deployed. Ratiu was taken into custody at that time.

Michael Schultz is the DA’s assigned victim-witness advocate. Ratiu is represented by attorney Neni Odiaga.