Police said Monday that someone had jumped from a moving train in the 100-block of West 69th Street on the South Side just before 2:40 p.m.
Police said another train hit him after he landed on the tracks.
He was pronounced dead on the scene.
CPD said Tuesday that three suspects pushed the person from the train during an altercation.
Red Line service was suspended between Garfield and 95th Street after the incident.
Trains were only operating between Howard and 47th streets.
Trains were later running with delays and running normally Monday night.
Area One detectives are investigating.