BEAUMONT, Texas (AP) — Seven inmates have been charged with killing two fellow prisoners and wounding two others during a January attack at a federal prison in Texas that led to a nationwide lockdown of the federal prison system.

The 15-count indictment filed this week includes charges of racketeering, murder and attempted murder against Juan Carolos Rivas-Moreiera; Dimas Alfaro-Granados; Raul Landaverde-Giron; Larry Navarete; Jorge Parada; Hector Ramires; and Sergio Sibrian.

The seven remain in federal custody and court documents do not list attorneys who could speak on their behalf.

The Jan. 31 attack was inside USP Beaumont in Beaumont, Texas. Prosecutors say the seven are members of the violent MS-13 gang and attacked rival gang members of the Mexican Mafia and its affiliate, the Sureños.

“Deterring prison violence remains a priority for the Department,” U.S. Attorney Brit Featherston of the Eastern District of Texas said in a statement Thursday. “Any prisoner who causes physical injury to another, inmate or corrections officer, will be prosecuted to the fullest extent of the law.”

Each of the seven could face the death penalty if convicted on the murder charges, the indictment states.

According to the indictment, the MS-13 maintained a relationship with the Mexican Mafia and Sureños for protection in prisons.

“However, that symbiotic relationship recently began to fall apart as MS-13’s leadership in El Salvador sought to exert more control and independence of its own members while incarcerated in prisons within the United States,” the indictment stated.

The change led the seven to conspire to kill members of Mexican Mafia and the Sureños, according to the indictment.

The indictment said Sureños member and Mexican Mafia associate Guillermo Riojas and Sureños member Andrew Pineda were fatally stabbed during the attack and two Sureños members were wounded.