HELENA, Mont. -- Former NFL quarterback Ryan Leaf has been moved from a drug treatment center to the Montana State Prison for threatening a staff member and violating his treatment plan, a corrections official said Thursday.

The former San Diego Chargers and Washington State Cougars quarterback was charged last spring with breaking into two houses and stealing prescription painkillers near his hometown of Great Falls. He pleaded guilty in May to burglary and criminal possession of dangerous drugs, and his five-year sentence called for spending nine months in a locked drug treatment facility as an alternative to prison.

Ryan Leaf, pictured here in his 2012 booking photo for breaking into two houses and stealing painkillers, was moved from a drug treatment center to the Montana State Prison for threatening a staff member and other behavioral problems. Getty Images/Cascade County Sheriffs Office

Leaf said then that he was looking forward to the treatment at Nexus Treatment Center in Lewistown. But on Thursday, the Montana Department of Corrections released a statement by Great Falls regional probation and parole administrator Dawn Handa that said Leaf will now serve his sentence in the Deer Lodge prison.

"The Montana Department of Corrections terminated Leaf from the treatment program and placed him in prison after he was found guilty of behavior that violated conditions of his drug treatment program. The violations included threatening a program staff member," Handa said in the statement.

Leaf attorney Kenneth Olson did not return calls for comment.

Adult Community Corrections Division director Pam Bunke wrote that Leaf was too great a security risk to leave in a community setting, and that staff had exhausted all resources in keeping him there.

Leaf told his roommate at the treatment center that he wanted to drag a program staffer by his hair, according to the Department of Corrections document approving Leaf's transfer to prison.

Leaf also wrote in three "Thinking Error Reports" that he wanted to throw the staffer against the wall and smash his glass into the man's head.

Thinking Error Reports are part of the treatment program meant to help participants monitor their potential problems and help them recognize and cope with the source of their addiction, according to an agency description.

Leaf was moved out of the Lewistown center on Dec. 29. He was held in the Fergus County Jail until he was transported to the Deer Lodge prison Wednesday, said Corrections spokesman Bob Anez.

A disciplinary hearing was held Jan. 9 in which a hearings officer found Leaf guilty of threatening another person or his possessions, according to a summary by the Department of Corrections.

He also was found guilty of wearing clothes he was told not to wear and volunteering his services when directed not to, according to the summary.

Those may seem to be minor charges, but it represented the fourth therapeutic action plan given to Leaf to try to bring him into compliance, the report said.

When Leaf was served papers for the hearing, he was "less than cooperative," according to the report.

"He got angry, swore at staff, refused to sign off on the witness form and threw the hearing notification papers on the floor," the report said.

Leaf will remain in the state prison until at least June 30, when he becomes eligible for parole, Anez said. That does not mean he will be released, but he will receive a hearing before the state Board of Pardons and Parole.

James Farren, the district attorney in the Texas county where Leaf was previously given probation in a plea agreement for drug charges in 2010, said his office will move to bring Leaf back to Randall County, where he could stand trial. The original Texas case stems from accusations that Leaf stole prescription pain medicine from a player's home while he was a coach at West Texas A&M.

If Leaf ends up getting prison time from a judge in Texas, he would return to Montana to serve out his time there. He would get credit for his Montana prison time in Texas, Farren said.

Farren said he gave Leaf a chance with the Texas plea deal. The Montana courts gave him another chance, he said.

"It doesn't matter how many chances he gets," Farren said.

Leaf was the No. 2 pick in the 1998 NFL draft, but his short-lived pro career earned him the reputation as one of the biggest busts in NFL history.

An investigation began in March 2011, after Great Falls postal workers reported they were suspicious of frequent packages Leaf received by paying COD charges of $500.

Central Montana Drug Task Force officers and Leaf's parole officer confronted the former quarterback and found a container with 28 oxycodone pills inside and another container with a prescription made out to an acquaintance.

The acquaintance said Leaf had entered his home without permission, and Leaf was arrested.

Shortly after his release, two Cascade County residents told authorities they found Leaf inside their home.

The couple reported three different prescription medications missing.

The Great Falls Tribune first reported Leaf's imprisonment Thursday.