HELENA, Mont. (AP) - Police in Montana arrested ex-NFL quarterback Ryan Leaf after a monthlong investigation that culminated with Leaf breaking into an acquaintance's home to steal prescription pain medication, the task force commander who led the probe said Saturday.

Authorities believe he may have broken into other homes in search of prescription drugs over the past 1 1/2 years and are asking those victims to come forward, said Central Montana Drug Force Commander Chris Hickman.

``We do have some information that this may not be an isolated incident,'' Hickman said.

Leaf faced a similar accusation in 2008, when he was accused of burglarizing a player's home while he was a quarterbacks coach for Division II West Texas A&M. An investigation turned up that Leaf had obtained nearly 1,000 pain pills from area pharmacies in an eight-month span. He reached a plea agreement that gave him 10 years' probation.

The prosecutor in that case in 2009 said he'll file a motion on Monday to revoke Leaf's probation following his Montana arrest.

``I think it's sad,'' said Randall County District Attorney James Farren. ``While I hoped for better results, I'm not surprised it happened.''

Leaf was arrested Friday in his hometown of Great Falls and charged with burglary, possession of a dangerous drug and theft. He is free on $76,000 bail and is scheduled to make a court appearance on Monday.

Leaf did not respond to text and voicemail messages left Saturday

Hickman said the task force's investigation began about a month ago when postal workers in Great Falls tipped police that Leaf had been receiving c.o.d. packages once or twice a week worth $500 or more.

The packages were small, they rattled and they were sent from a Florida address that turned out to be a mailbox company, a favored method for distributing illegal prescriptions, Hickman said.

Police were familiar with Leaf's history of prescription medication problems, so they kept watch and decided to act when the packages began to arrive more frequently.

``We felt it was necessary to confront him as soon as possible before it got any further out of hand,'' Hickman said.

Task force members on Friday told Leaf's probation officer to call in the ex-quarterback. They searched Leaf and his truck, finding two prescription bottles in a pocket of a golf bag, which was embroidered with Leaf's name.

One unlabeled bottle had 28 pills that turned out to be oxycodone, a schedule 2 narcotic for which Leaf does not have a prescription. The other was empty but its label said it was oxycodone prescribed for another person, Hickman said.

That person, whom Hickman did not name, is an acquaintance of Leaf's. Police interviewed him, his live-in girlfriend and his housekeeper, and concluded that Leaf entered the house without permission on Thursday afternoon and took the man's prescription medication.

Leaf knocked on the man's door, then entered without waiting for an answer, Hickman said. Leaf surprised the housekeeper, the only person home, and told her that he was a friend of the owner and had some business to take care of.

The owner discovered his pills missing Thursday evening and called Leaf to confront him, asking him to return the pills, which he never did, Hickman said.

The owner said there were about 15 pills in the bottle, meaning police don't know where the 13 others in Leaf's possession at the time of his arrest came from, Hickman said.

Police also searched Leaf's home but did not find any more painkillers or any evidence from the packages he had been receiving in the mail.

Leaf told police that he had been receiving medication through the mail for which he has a prescription, but he did not provide proof, Hickman said.

``We established from Mr. Leaf that he was receiving prescription medication from this company but we're still not sure what they are,'' Hickman said.

Leaf released a statement through his publicist, Wendy Ogunsemore, on Friday night.

``I've made some mistakes, and have no excuses,'' the statement read. ``I am using the tools I've learned to move forward rather than backwards, and will be open to talking about the details in the days to come. I am confident that there will be further understanding when the facts are revealed, and feel very blessed for all of the support, especially from my friends and family.''

Leaf, a former standout quarterback for Washington State, was the No. 2 pick in the 1998 draft behind Peyton Manning. But Leaf flamed out as quarterback for the San Diego Chargers, gaining a reputation as one of the biggest busts in NFL history.

Leaf's defense attorney in the Texas case, Bill Kelly, said Saturday that he hadn't spoken to his client. Leaf's father, John Leaf, called Kelly on Friday to tell him about the arrest, he said.

``His dad was pretty upset, of course,'' Kelly said. ``People get hooked on these things and it's hard to get off of them. It's just a sad, sad deal because he was doing so well.''

Last year, Leaf had surgery to remove a benign tumor from his brain stem and later underwent additional radiation treatments.

On March 21, Leaf told an Associated Press reporter in an email exchange that he had struggled through treatments and had an MRI scheduled for the end of the month, but ``I'm doing/feeling much better and am excited for the rest of 2012.''

Farren said if the Texas judge revokes Leaf's probation, he could go to prison for longer than the 10-year probation term. The judge could treat each of Leaf's drug charges in Texas - seven counts of obtaining a controlled substance by fraud and one count of delivery of a simulated controlled substance - separately because that's the way the plea deals were done, he said.

Some of the charges carry a sentence of up to 20 years in prison.

``The judge could stack them,'' Farren said.

Last year, Leaf wrote a book titled ``596 Switch'' - the name of a passing play in the Washington State playbook - that focused on the 1997 season when he led the Cougars to their first Rose Bowl in six decades.

Seattle communications consultant Greg Witter, a friend of Leaf's who co-authored the book, said Saturday that Leaf has been ``diligent'' about fighting his addiction, including admitting himself to rehab around Christmas 2010 when he saw inklings of his old behaviors surfacing.

``I'm hopeful this is a misunderstanding of some kind and that Ryan can continue making the great strides in his life that we've all seen over the last three years,'' he said.

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Blaney reported from Lubbock, Texas.