A Roslindale youth was held without bail today as he was formally charged with the murder of 21-year-old Richard Allen on board an MBTA bus last fall, Suffolk County District Attorney Daniel F. Conley said.

In addition to being held for Allen’s fatal stabbing, KIM GROSS, Jr. (D.O.B. 12/7/92), was held on $25,000 cash bail for allegedly stabbing a second victim non-fatally during the same Nov. 2 incident on a Route 44 bus near the intersection of Humboldt Avenue and Wyoming Street.

At the defendant’s Roxbury District Court arraignment, Assistant District Attorney John Pappas told the court that shortly before 9 on the morning of the incident, Gross and an associate boarded the Route 44 bus and took seats in the rear. A short time later, Pappas said, Allen and two of his associates also boarded the bus. Allen sat down next to the defendant, and one of his associates also took a seat at the rear of the bus. The third person went to the rear of the bus with the others, but didn’t sit.

Shortly after the three men boarded, Pappas said, a member of Allen’s group got into a brief verbal exchange with the defendant. During this verbal exchange, an uninvolved party observed a distinctive scar on the defendant’s right hand.

Moments after the verbal exchange, Pappas said, the person described by witnesses as having a scarred right hand – identified by authorities as Gross – produced a knife and stabbed Allen once in the chest, perforating a major artery and his esophagus, causing fatal injuries. After mortally wounding Allen, Pappas said, Gross then proceeded to stab a second member of Allen’s group numerous times. That individual was seriously wounded, but survived his injuries.

During the course of an extensive and ongoing investigation conducted by Boston Police homicide detectives, MBTA Transit Police detectives, and Suffolk prosecutors, investigators were able to evaluate data collected from the bus’ fare box and witness accounts that identified Gross as the individual with significant scarring on his right hand.

Gross was arrested Friday and faces additional weapons and narcotics charges for a gun and drugs recovered from the car in which he was travelling. He is expected to be arraigned in West Roxbury District Court on those charges in the near future.

Gross is the second person to be arrested this year for a Boston homicide committed last year. LAVONRENCE PERKINS (D.O.B. 3/26/90) was arrested Jan. 18 for the May 7, 2010, shooting death of Cordell McAfee.

Catherine Rodriguez is the DA’s assigned victim-witness advocate. Gross is represented by attorney James Greenberg. Judge David Poole ordered him to return to court on March 16.