Forest Park is a Chicago suburb in Cook County 10 miles west of the city.

Police are not releasing the name of the suspect. They have said a 911 call was received prior to 5:30AM and responding officers found four victims. Three had died at the scene and one died later at the hospital while being treated.

The suspect fled and was later apprehended. The accused suspect was found on another train line, the Pink Line, with a firearm.

Guns are not allowed to be brought onto any property owned by the Chicago Transit Authority. Transit areas are a "gun free zone" in Illinois.

Just four days ago, the Chicago Transit Authority was bragging about its extensive use of security cameras and anti-gun technology to 'spot' and 'detect' guns.

Chicago is one of the most gun-hostile jurisdictions in America. Generally speaking, Chicago tries to ban all possession of handguns.

Illinois state law specifically prohibits gun possession on any property owned by a public transportation agency.

Anti-Gun groups like the Everytown/Brady Center group rank Illinois as #3 in the nation for "gun law strength" meaning how hostile it is to gun ownership.

The anti-gun group the Giffords Law Center gives the State of Illinois an "A-" for the degree to which they restrict gun ownership and possession. The Giffords Center is named for former Congresswoman Gabrielle Giffords who was shot in the head by former Quiznos employee Jared Loughner in Tucson in 2011.

Police say that this shooting at Forest Park is an isolated incident, even though Chicago has gone through a remarkable rise in violent crime.