In Wednesday’s shooting, police say that about 50 people were on the train at the time and that about a dozen people witnessed some or all of the fight between Oates and Boone. There was no video surveillance available from the train, Metro said.

Neither Boone nor Oates was an UMSL student, police say. Investigators were still trying to determine whether the men knew each other.

When the train stopped, the doors opened and the gunman raced off, running south on the tracks. Police officers caught Oates within minutes and recovered a gun.

Oates lives in the 6700 block of Thurston Avenue in Berkeley, police said. He is on probation for robbing someone at gunpoint of a PlayStation on Oates’ 16th birthday. That crime took place in Florissant in 2014. Oates was certified to be charged as an adult. Court records show he pleaded guilty in February 2016, received a suspended execution of sentence and was put on five years’ probation.

As to what led to Wednesday night’s fatal shooting, St. Louis County police Officer Benjamin Granda said. “We do not have any type of motive for the incident at this time.”