18-year-old Matthew Early was arrested Friday evening at a friend's house in North Philadelphia.
Police say Early and his brother, 17-year-old Eric Early, had argued with a Chicago Bulls fan on the Market-Frankford Line after the 76ers lost to the team on Dec 12.
Authorities say Matthew Early fired through the train's open doors as he exited at the 46th Street station, hitting two people.
Eric Early has been in custody since Dec. 17. He's charged as an adult with aggravated assault and other offenses. The charges against Matthew Early weren't immediately clear.
It could not be determined if either suspect has a lawyer.