The mass shooting in Five Points South that left four people dead and 18 others injured Saturday night may have been a contract killing, Birmingham’s police chief said at a press conference Sunday morning.

Officer Truman Fitzgerald said the shooting occurred shortly after 11 p.m. in the 2000 block of Magnolia Avenue South. More than 100 shell casings were found at the scene.

Two men and a woman were pronounced dead at the scene. A fourth victim died at UAB Hospital.

Police said no suspects were in custody yet and that ATF and FBI had been called in to assist in the investigation.

Police Chief Scott Thurmond said their sincere condolences go out to the families of the dead and the many injured.

“These are 21 people whose lives have been changed forever,” Thurmond said.

Thurmond said police received information that the shooting may have been a contract killing. “Wherever that (target) person was, that’s where it would have taken place,” Thurmond said.

Thurmond said several shooters drove up in a car, got out, fired shots and then drove away.

Mayor Randall Woodfin said the public must provide information to police and the state and nation must address what he sees as lax gun laws.

“This is a solvable problem,” Woodfin said. “Gun violence is an epidemic crisis in our country… We all need to stand together.”

“I want to work with the state to solve the problem,” Woodfin said. “I’m not here to point fingers.”

See also: A look at other mass murders in Alabama

Initial reports said clubbers were waiting in line outside Hush, a hookah and cigar lounge on Magnolia Avenue, when the shooting occurred. Witnesses said at least some of the gunfire sounded like it came from a weapon equipped with a “switch” that turns a gun into a fully automatic weapon.

Firefighters rescued eight injured people from the scene of the accident. The other victims were taken to hospitals in Birmingham.

“We have dozens of gunshot victims from this area,” Fitzgerald said. “I’ve been told that at least four of those gunshot victims are in critical condition.”

Investigators believe that several shooters fired numerous shots at the group of people on Magnolia Avenue.

You can submit information to police here. You can also call investigators at 205-254-1764 or Crime Stoppers at 205-254-7777.

This is a developing story and will be updated.