A 25-year-old Delta man suffered a broken jaw and other injuries in a brutal beating aboard a SkyTrain at Columbia Station in New Westminster July 6.
The assailant asked the victim, who had just boarded the train, about CDs and then began punching him in the face and head, according to Transit Police.
A woman with the Delta man hit the yellow silent emergency alarm strip, alerting officers.
The suspect and his companion jumped off the train and fled, but Transit Police were able to arrest a 21-year-old man of no fixed address a short time later in New Westminster.
Kyle Alain-Boya is charged with aggravated assault and is being held in custody pending a July 9 court appearance.
The victim, who also suffered fractured teeth, cuts to his face, a black eye and other deep bruising, underwent surgery at Royal Columbian Hospital.
Transit Police said the woman's act of pressing the emergency strip helped immediately alert police to a serious incident and their exact location, ensuring the victim got rapid assistance and helping lead to the arrest of the suspect.