(CNN) — On a Chicago transit train, four individuals who looked to be asleep were shot and killed on Monday morning, according to the police. Chris Chin, the deputy chief for Forest Park, stated, "The victims were all passengers on the train early this morning." "As the train entered Forest Park, it was moving."
Chin told CNN that the victims could have been homeless. 
"We are unsure of their exact socioeconomic standing. They were dozing off on the train, based on the recordings, Chin added.
Police believe the mass shooting to be an isolated event or random act, and they have detained a person in connection with it.
The Chicago Transit Authority and investigators are collaborating to examine security footage from the incident, which occurred in two train carriages, according to the police: three people were in one vehicle and four people were in another.
The culprit, who was apprehended around one and a half hours after the gunshot, was identified, according to police, thanks in large part to security footage.
"The CTA's cameras are excellent. They have really good security cameras," Chin said.
Chin claimed that in order to find and apprehend the offender, three organizations collaborated: the CTA, Chicago Police, and Forest Park Police.
Chin informed CNN The suspect most likely got off the train at the CTA Blue Line's Harlem stop. Eventually, he made his way to the Pink Line, where police were waiting to arrest him. A gun was also retrieved by law police.
"After watching a few of the films, it appears that they were able to track, find, identify, or at the very least, pinpoint... Alright, Forest Park is searching for this person. Chicago managed to capture him, and we swiftly intervened to apprehend him.
The transport authority stated in a statement that "even though this was an isolated incident, this heinous and egregious act of violence should never have occurred, nonetheless on a public transit train."
Prosecutors will have 48 hours from the moment of the suspect's arrest to declare any charges against him while investigators go over the evidence.
Chin remarked, "This is obviously shocking—you know, mass shootings like this are not common." Since this is a singular incidence, it may occur anywhere. Because it is on a public transportation system, there is a little bit more worry," he continued. "It's okay for people to feel unsafe."
The 27-mile CTA Blue Line runs from O'Hare International Airport to Forest Park, going through or close to several communities as well as Chicago's downtown.
At a press conference, Forest Park Mayor Rory Hoskins stated that the police and fire departments respond to the same area of the park "probably more than any other location in our jurisdiction." He then made a plea to the state government for more law enforcement and public safety workers.
He claimed to have visited Springfield previously to advocate for increased funding for treating opioid addiction and mental health issues.
The mayor called this incident a "outlier," claiming that there hasn't ever been a shooting of this nature in the city before.
According to the Gun Violence Archive, which, like CNN, defines a mass shooting as one with four or more victims, not including the gunman, Monday's shooting is one of 381 mass shootings that have occurred in the US so far this year. In the United States in 2024, there were 1.5 mass shootings on average per day.
Chicago police stated in a statement that another passenger on the Red Line suffered critical injuries in a stabbing that occurred hours after the gunshot. The victim, 37, and the unidentified male got into a verbal fight before the assailant pulled out a "sharp object" and stabbed the victim many times, according to the police.
"At the Wilson Red Line station, the victim escaped the train and made his way on foot to the 4700 block of North Broadway." After that, the woman was taken to Illinois Masonic Hospital, where she was first declared critically ill, according to police, who spoke with CNN.
Detectives are looking, but no suspect has been located yet.