According to boston.com, this is what they think now:
Cable failure apparently caused by old wiring sparked a fire in a Red Line tunnel at South Station around 6:35 p.m., according to the Massachusetts Bay Transportation Authority.
At about the same time, T officials suspect that a customer threw debris onto the third rail of an Orange Line track in the tunnel at the Chinatown station, sparking a second fire.
no subject
Cable failure apparently caused by old wiring sparked a fire in a Red Line tunnel at South Station around 6:35 p.m., according to the Massachusetts Bay Transportation Authority.
At about the same time, T officials suspect that a customer threw debris onto the third rail of an Orange Line track in the tunnel at the Chinatown station, sparking a second fire.