The FBI arrested multiple California police officers on Thursday as part of a major criminal investigation into racist text messages of dozens of law enforcement officials, prosecutors said.

Early-morning federal raids rounded up officers from Antioch and Pittsburg, two cities east of San Francisco, after a grand jury indictment for a wide range of offenses including criminal conspiracy, the Bay Area News Group reported. The charges remained sealed on Thursday morning, and it’s unclear how many officers have been arrested and are facing prosecution. A spokesperson for the US Department of Justice confirmed to the Guardian that arrests have been made and court hearings in the case were ongoing, but declined to comment further.

The arrests come after revelations that Antioch officers sent violently racist, misogynistic and anti-gay text messages between 2019 and 2022. The hateful messages emerged as part of an inquiry by federal officials and local prosecutors investigating claims of widespread civil rights violations, excessive force and falsification of records.

Officers were exposed referring to Black people as “gorillas” and bragging about beating up local residents and fabricating evidence. Some group texts included supervisors. In April, it was revealed that more than 45 officers, representing nearly half of Antioch’s police department, were implicated in racist behavior.

The Bay Area News Group, which first exposed the text messages, reported that the indictments this week include conspiracy to commit wire fraud, conspiracy against rights, deprivation of rights, and falsification or destruction of records. One officer who appeared in court on Thursday could face up to 20 years in prison on the records destruction charge alone, the publication reported.

Prosecutors have been forced to drop or dismiss dozens of cases that involved the officers who were exposed, and the local county has assigned attorneys to review thousands more files, according to the publication.

“Not only do we have officers who have fundamentally racist ideas and disrespect for the community, but they’re dishonest, too, and that goes to the very integrity of the criminal justice system,” said John Burris, a civil rights attorney who has brought a class-action case against Antioch police. “There was a kind of lawlessness in the department, and there was no accountability. There was a code of silence. These officers understood that there was a freedom to engage in this conduct without having any repercussions and that’s a failure of leadership.”

Antioch’s mayor, Lamar Thorpe, said in a statement that it was “a dark day in our city’s history, as people trusted to uphold the law, allegedly breached that trust and were arrested by the FBI”. Elected in 2020 on a platform of reform, he added: “To those that have accused me and others of being anti-police for seeking to reform the Antioch police department, today’s arrests are demonstrative of the issues that have plagued the Antioch police department for decades.”

An Antioch police spokesperson declined to comment.