BOISE, Idaho (AP) - The FBI has taken over the Idaho criminal investigation into private prison company Corrections Corporation of America.

The Nashville, Tenn.,-based CCA has operated Idaho's largest prison for more than a decade, but last year, CCA officials acknowledged it had understaffed the prison 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 earlier this year.

Idaho Department of Correction spokesman Jeff Ray confirmed Friday that the FBI has interviewed depar tment director Brent Reinke, and Idaho State Police spokeswoman Teresa Baker said her agency was no longer leading the investigation.

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 spokesman Steve Owen has said the company believes the audit overestimates the staffing issues by more than a third.

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 prison 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 th e 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.

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.