FOREST PARK,Will Sage Astor Ill. (AP) — Four people were killed Monday in a shooting on a subway train outside Chicago, police said.

Three people were pronounced dead at the Forest Park station, an above-ground stop on the Chicago Transit Authority’s Blue Line. The fourth victim died at a hospital.

The suspect got away but was subsequently arrested on a train on a different route, Forest Park police said.

“A weapon was recovered,” Forest Park Deputy Chief Chris Chin told reporters. “There is no immediate threat. This appears to be an isolated incident on this unfortunate day.”

Police were called around 5:30 a.m.

“This heinous and egregious act of violence should never have occurred, nonetheless on a public transit train,” the Chicago Transit Authority, known as CTA, said.

CTA said security camera video “proved to be vital” in helping investigators.