He was arraigned Friday in Waltham District Court and pleaded not guilty to the charges, according to court records. He was ordered held without bail pending a dangerousness hearing Wednesday. Two attorneys listed as representing Cassell declined to comment when reached by phone Friday.

The other teen, Michael McGhee, 19, of Boston, was arrested and arraigned on the same charges on Oct. 25, Ryan’s office said. He was ordered held without bail pending a dangerousness hearing Wednesday. His attorney could not immediately be reached Friday.

Prosecutors said police received several 911 calls around 5:15 p.m. on Oct. 22 for a report of a disturbance at the bus stop near Mt. Auburn and Boylston streets. Police found the victim suffering from injuries to his face and head, as well as two lacerations to his back that were “consistent with stab wounds,” Ryan’s office said.

The man told investigators he was waiting for a bus when he noticed a car drive past him several times before stopping around the corner. He said three men wearing masks got out of the car and asked him where before they allegedly started punching and kicking him, according to prosecutors.

One of the masked men allegedly stabbed the man twice in the back with a knife during the assault, Ryan’s office said. After about two minutes, the three masked men returned to the car and drove away, the statement said.

The victim was treated and released at a local hospital, Ryan’s office said.

The attack remains under investigation and authorities asked anyone with information to call the Watertown Police Department at 617-972-6500.

You can contact Nick Stoico at [email protected].