"The Mexican Mafia is a violent criminal gang. They deal in intimidation. They deal in drugs — heroin and cocaine. They deal in violence, and in this case, they dealt in murder," he said.
The slayings go back to 2000 and occurred in San Antonio, Austin and Atascosa County, a rural county south of San Antonio. Most were unsolved before the racketeering charges, said Sutton.
The victims were mostly members of the Mexican Mafia or rival gangs. In some cases, they were suspected drug dealers indebted to the Mexican Mafia, which authorities say enforces a street tax on drug dealers who work on gang turf.
The defendants were not charged with murder, in part because tying them to a specific crime is harder than proving they ran an operation that committed murder and dealt drugs, Sutton said. Conviction under federal racketeering charges can bring a term of life in prison.
Most of the defendants were already in custody on lesser charges before the Tuesday grand jury indictment, which was first reported by the San Antonio Express-News. By Wednesday morning, 18 were in custody. Another five were still being sought.
None had attorneys listed in U.S. District Court filings.
The investigation that led to Tuesday's indictment included the use of informants and undercover officers over a three-year period, said Sutton, though he declined to release details of the investigation. Other indictments could still be coming, he said.
FBI Special Agent In Charge Ralph Diaz called the indictments, which included alleged generals and lieutenants in the gang, "a very significant hit to the organization."
The Texas Mexican Mafia, allegedly founded by San Antonio native Heriberto "Herb" Huerta in 1984, is the largest gang in the state prison system, but it's not directly related to a California gang of the same name. Huerta and other gang members were later convicted on drug charges.

The Texas Department of Criminal Justice tracks the number of Mexican Mafia members in the prison system but doesn't release the numbers because of concerns that it will exacerbate problems with rival gangs in the system, said department spokesman Jason Clark.
Gangs like the Mexican Mafia recruit members inside the prison system as a way to ensure protection, but membership continues even when an inmate is released, said FBI spokesman Eric Vasys. Some members are also recruited among family or friends who not incarcerated.
Outside prison, the gang allegedly deals drugs and extorts people. Members also carry out retaliatory killings or other violence at the orders of bosses, many of whom are still in prison, Vasys said.
The federal racketeering law provides a way for prosecutors to go after gang members even if they didn't directly commit a violent crime.
"You don't have be there to get convicted," Vasys said.
While most of the victims in this week's indictment were gang members or drug dealers, authorities said the crimes affect neighborhoods and innocent family members.
Even if it's "bad guy killing bad guy, it still deteriorates the fabric of the community," said Vasys.