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A celebrity Web site released a recording Monday that appears to capture an agitated O.J. Simpson shouting expletives and threatening sports memorabilia collectors in a hotel room here last week, as he tried to take back mementos he claimed were his.

“Think you can steal my property and sell it?” a man believed to be Simpson angrily says on the audio obtained by TMZ.com after it was surreptitiously taped by auctioneer Thomas Riccio, who had arranged for Simpson to meet with men who reportedly were trying to sell his mementos.

The recording appears to capture a far-more menacing confrontation than the one Simpson, 60, described in interviews after the Thursday incident.

Las Vegas authorities, who are holding Simpson behind bars pending formal charges related to the alleged armed robbery, said they could not confirm the recording’s authenticity.

But one of the two sports memorabilia dealers who was in the hotel room with Riccio when Simpson allegedly burst in with an armed entourage said it sounded like what he witnessed.

“It’s definitely audio from that room, though I’m not sure if it has been edited,” said Alfred Beardsley, a collector who said he was trying to broker a sale for the man in possession of the items, collector Bruce Fromong.

Beardsley accused Riccio of setting up the confrontation for personal gain.

“Riccio said he had a guy who was just a huge, huge O.J. fan, who wanted anything he could get. I now see that I was brokering a deal with someone who didn’t exist. It was an O.J. sting,” he said. “It was a robbery; they came in with guns. I feel bad because I could have gotten Bruce killed.”

Riccio, an auctioneer based in Corona, Calif., who recently was involved in selling the diaries of the late Playboy model Anna Nicole Smith to a German businessman for $500,000 — said Monday that he hid a recording device in the room at the Palace Station Hotel & Casino because he wanted evidence that Beardsley and Fromong were trying to sell stolen merchandise.

“I wanted it on tape in case Beardsley denied it when O.J. came in,” Riccio said.

He said the device was still recording when police conducted interviews in the room — after Simpson and some associates allegedly barged in at gunpoint.

The football legend has said he was trying to recover memorabilia from his professional and college playing days, as well as personal photos, that had been stolen by a former agent.

Riccio insinuated he had given the recording to TMZ.com but was evasive when asked whether he had been compensated for it.

He said he mailed a copy to Las Vegas police Sunday.

The only other person arrested in the alleged armed robbery is Walter Alexander, 46, of Arizona, who was released Sunday without bond after speaking with prosecutors. His lawyer said Monday that Alexander hadn’t cut any deals with prosecutors, and was unclear whether he would be a government witness in any trial.

Simpson cannot be held longer than 72 hours without being formally charged, said Clark County Judge Nancy Oesterle, who was assigned Monday to field questions from the media circus assembling in Las Vegas.

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Held without bail

Since his arrest Sunday, O.J. Simpson has been held — without bail — in a cell 7 feet by 14 feet with one bunk bed, a toilet, a desk and a window, officials said.

He has been visited by several lawyers and a minister, who brought a Bible, the book “The Purpose-Driven Life” and two pairs of reading glasses.