A fourth man has been arrested after the deadly shooting at a 16th birthday party in Alabama that left four dead and 32 injured last Saturday.
Johnny Letron Brown, 20, was arrested on Thursday and formally charged with four counts of reckless murder.
Brothers Ty Reik McCullough, 17, and Travis McCullough, 16, were arrested on Tuesday night. Wilson LaMar Hill, 20, was held on Wednesday afternoon.
Police have still not disclosed a potential motive for the shooting.
At least four people between the ages of 17 and 23 were killed at the birthday party in the small city of Dadeville. There were about 50 people at the celebration, which was held at a local dance studio.
The suspects are each being charged with four counts of reckless murder, police said.
Officials said the four suspects are from Tuskegee, Alabama, which is about a 40-minute drive from the crime scene in Dadeville.
The two teenagers will be tried as adults, an automatic requirement for anyone 16 or older charged with murder in the state.
At a press conference on Wednesday, officials told reporters the investigation was still in its early stages.
District Attorney Mike Segrest said: “I know that there has been some frustration among our community and among media about a lack of information that has been provided up to this point.”
Officials previously said they had recovered shell casings used in handguns at the crime scene, noting that there was no evidence a high-powered rifle had been used.
Police said Wednesday that among those injured, four remained in hospital in a critical condition.
“We are going to make sure every one of those victims has justice and not just the deceased,” Sgt Jeremy Burkett of the Alabama Law Enforcement Agency (ALEA) said.
The agency added: “These individuals have been charged after a complex and thorough investigation was conducted with assistance from a multitude of law enforcement agencies.”
The deceased victims have been identified as Marsiah Collins, 19; Phil Dowdell, 18; Corbin Holston, 23; and Shaunkivia Smith, 17.
Mr Dowdell died trying to save his sister Alexis, his family has said. He was a star athlete on his high school’s American football team and had been due to graduate to go to Jacksonville State University on a sports scholarship.
One of his friends and school football teammate told the BBC: “Phil to me was an amazing friend. God’s got an angel.”
Dadeville, a town of roughly 3,000 residents, is about 60 miles (100km) north east of the state capital of Montgomery.
Sgt Burkett urged those who were at the party at the dance studio to contact authorities if they have not already done so.
“We need you to come forward for these families, for these victims,” he said.
The weekend attack took the US to a grim milestone of more than 160 mass shootings this year, according to the Gun Violence Archive, which defines such events as ones in which four or more people are shot.