Police told CBC News that a group of five young people were in the area of a Dundas Street West and Sterling Road underpass at the time of the incident.
The four other youths were scared and fled after the accident, which occurred minutes after a GO Train left Union Station on Monday evening. They have since been tracked down and interviewed by police.
Police say that video from the train leaves no doubt as to what happened. The death was accidental, the teenager stumbled and fell onto the tracks.
The deceased has been identified as 17-year-old male. His family has been notified and police are not releasing his name.
However, CBC News has learned that Tyler Bailey is the teenager who was killed on Monday evening.
The teen was an accomplished scooter rider who spent many of his weekends at a skateboard park in Etobicoke.