Officials confirmed that four people were killed in a shooting early Monday on a Chicago Transit Authority train in Forest Park, Illinois.

The Forest Park Police Department said in a Facebook post that they received a 911 call around 5:27 a.m. about three people shot on a westbound train at the CTA Blue Line station at 711 Desplaines Avenue, Forest Park, just west of Chicago, around 5:30 a.m. local time. Authorities cleared the station, finding four victims — three were pronounced dead on scene, and the fourth was taken to Loyola University Medical Center in Maywood, where they died.

Forest Park police, along with CTA security, used video surveillance to help identify the offender; with Chicago Police later locating the suspect who matched the description on a CTA Pink Line train. The subject was taken into custody and a firearm was found. According to Forest Park officials, only one suspect is believed to have been involved in the shooting, which was targeted.

The CTA said in a Monday afternoon news briefing that the incident was a “heinous and egregious act of violence” that “should never have occurred, none the less on a public transit train. As soon as it was reported, CTA immediately deployed resources to assist the Forest Park Police in their investigation into the matter, including review of all possible security camera footage, which proved to be vital in aiding local enforcement.”

The CTA said it will continue to work with local law enforcement regarding the ongoing investigation.

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