A shooting on a Labor Day morning train in a suburb of Chicago has resulted in four fatalities, with a suspect now in custody, authorities reported on Monday.

According to police, the alleged shooter was arrested on Monday evening.

The Forest Park Police Department received a 911 call just before 5:30 a.m., indicating that three people had been shot on a train at the Forest Park Chicago Transit Authority Blue Line Station, around 10 miles from downtown Chicago. When officers arrived, they discovered four individuals had been shot. Three were pronounced dead at the scene, and the fourth individual later succumbed to injuries at a local hospital, police stated.

Deputy Police Chief Christopher Chin shared with YSL News that the victims seemed to be sleeping on the train when they were attacked. The first three victims were in one train car, while the fourth was in a different car.

“It seems to be random,” Chin commented.

Initially, the shooter fled the scene, but police identified a suspect through surveillance footage. The suspect was found on a CTA Pink Line train and was taken into custody, with a firearm also recovered, according to the Forest Park police.

Victims and the suspect have not been publicly named yet. The motive for the attack remains unclear; however, Chin labeled it as an “isolated incident.” The suspect was apprehended around 7 a.m. Monday and is expected to face charges by Tuesday evening, although authorities have a 48-hour window to file charges.

Forest Park Mayor Rory Hoskins expressed his sorrow during a news conference, stating, “It’s a terrible tragedy that four people lost their lives on Labor Day weekend.” He mentioned that police often respond to the train station more frequently than any other location in town but do not encounter mass shootings often.

According to data compiled by YSL News, the Associated Press, and Northeastern University, over 3,000 individuals have been killed in 602 mass shootings since 2006.