Four people were killed and 18 more were injured in a shooting in Birmingham, Alabama, police said Sunday. Some of the individuals wounded suffered injuries “life-threatening injures,” Birmingham Police Officer Truman Fitzgerald told a news conference, hours after after the incident that occurred in what he called one of the city’s “most popular entertainment districts.”

Police said they believe multiple suspects fired at a large group of people standing outside near Magnolia Avenue in the Five Points South area, police said. The shooting happened just after 11 p.m. CST.

Two men and one woman were pronounced dead at the scene by Birmingham Fire and Rescue. Police officers found them lying unresponsive on a sidewalk when they arrived. Each had multiple gunshot wounds.

A fourth gunshot victim, another man, was pronounced dead by staff at University of Alabama at Birmingham Hospital. Police also identified him as an adult man.

Detectives believe the shooting wasn’t random. Police said in a statement that they think it “stemmed from an isolated incident where multiple victims were caught in the crossfire.” They were still working to determine who the shooting intended to target.

No one was in custody early Sunday morning, but Fitzgerald told reporters that police “will do everything we possibly can to make sure we uncover, identify and hunt down whoever is responsible for preying on our people this morning.” 

Police said they were investigating alongside the Bureau of Alcohol Tobacco and Firearms as well as the Federal Bureau of Investigation. They have asked anyone with information to contact the homicide division at the Birmingham Police Department or report tips anonymously to Crime Stoppers. The latter may give up to $5,000 for tips, according to police.

The University of Alabama at Birmingham campus is located in the Five Points South area, which is a nightlife hub in the city where numerous restaurants, bars and live music venues draw large crowds, particularly on weekend nights.