Two men and a woman were pronounced dead at the scene, which is near entertainment venues and bars near the University of Alabama at Birmingham, while a fourth victim, an adult male, died at the university’s hospital. Police said during a press conference on Sunday at least 21 people in total were shot.

At least 18 people were injured, with the University of Alabama at Birmingham Hospital receiving 11 of the victims, including one of the people who died, the hospital confirmed to CNN. At least four of the shooting victims have life-threatening injuries, according to Birmingham Police Officer Truman Fitzgerald.

Birmingham Police Chief Scott Thurmond said on Sunday that multiple people drove up to the Five Points South area just after 11 p.m. on Saturday, exited their vehicles, and began shooting. The suspects then returned to their cars and drove away.

Officers believe the shooting was a targeted “hit” on one of the deceased individuals, and the others were caught in the crossfire. Victims were all out in the open, either on the sidewalk or on the streets, police said. No suspects are in custody as of Sunday morning.

“That’s 21 people whose lives were forever changed. That’s 21 families that were, some were destroyed, and some were just altered,” Thurmond said. “Our hearts go out to them as we work through this.”

“Someone was willing to pay money to have that person killed,” Thurmond said via CNN.

Birmingham Mayor Randall Woodfin said gun conversion devices, sometimes called “switches” that allow a weapon to operate like a machine gun, were possibly used in the shooting.

Approximately over 100 shell casings were collected at the scene, Thurmond said.

The Birmingham Police Department, in partnership with the FBI and the ATF, is investigating and encouraging those with information to come forward.

This is the latest mass shooting to strike Birmingham, with a mass shooting defined by the Gun Violence Archive as an event in which at least four people are shot, not including the shooter.

In July, four people were killed and 10 others injured in a shooting at a nightclub, per local outlet WVRC. In February, four men were shot and killed outside a public library in the city, per local outlet WVTM.