The FBI has launched a criminal investigation into private prison company Corrections Corporation of America which ran what Idaho inmates called “Gladiator School” because of a violent reputation they say understaffing helped create.

The Nashville-based CCA has operated Idaho’s largest prison for more than a decade, but last year, CCA officials acknowledged it had understaffed the Idaho Correctional Center by thousands of hours in violation of the state contract. CCA also said employees falsified reports to cover up the vacancies. The announcement came after an Associated Press investigation showed CCA sometimes listed guards as working 48 hours straight to meet minimum staffing requirements.

The Idaho state police was asked to investigate the company last year but didn’t, until amid increasing political pressure, the governor ordered the agency to do so last month. Democratic state lawmakers asked the FBI to take up the case last month.

Idaho department of correction spokesman Jeff Ray confirmed Friday that the FBI met with department director Brent Reinke on Thursday to inform him about the investigation. Idaho State Police spokeswoman Teresa Baker said her agency was no longer involved with the investigation and the FBI has taken it over entirely.

"”They (the FBI) have other cases that are tied to this one so it worked out better for them to handle it from here,” Baker said.

CCA spokesman Steve Owen could not be immediately reached, but Owen has previously said that his company would continue to cooperate with any investigation.

The understaffing has been the subject of federal lawsuits and a contempt of court action against CCA. The ACLU sued on behalf of inmates at the Idaho Correctional Center in 2010, saying the facility was so violent that inmates called it “Gladiator School” and that understaffing contributed to the high levels of violence there.

In 2012, a Boise law firm sued on behalf of inmates contending that CCA had ceded control to prison gangs so that they could understaff the prison and save money on employee wages, and that the understaffing led to an attack by one prison gang on another group of inmates that left some of them badly injured.

The Department of Justice requested a copy of a forensic audit done for the Idaho Department of Correction earlier this year. That audit showed that CCA understaffed the prison by as much as 26,000 hours in 2012 alone; CCA is strongly contesting those findings. CCA’s Owen has said the company believes the audit overestimates the staffing issues by more than a third.

CCA’s contract with Idaho was worth about $29 million a year. In February the company agreed to pay Idaho $1 million to settle the understaffing claims.