In the video, a man identified as Husie Outing pushes a 14-year-old boy onto the Red Line tracks at the Pershing Square Station and then takes off.
Fire officials said the victim suffered some contusions and cuts but did not want to be transported.
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Police say when the suspect emerges from the station, he then assaults a construction worker. Several workers then held him down until officers arrived.
New body camera video shows officers arriving and placing the 47-year-old man under arrest. Officers can be heard saying that his head and hand are injured, and that they believe he's under the influence of some sort of narcotic.
Outing was taken to the hospital, where he later died.
His cause of death is pending the results of a toxicology test.