LAS VEGAS: The man who contends that O. J. Simpson stole $100,000 in sports memorabilia from him told a judge on Thursday that the former football star led a six-minute "military-invasion-fashion" raid in September in a Las Vegas hotel room.

Bruce L. Fromong, 53, a memorabilia dealer from North Las Vegas, spent more than three hours recounting the incident on Sept. 13 and fending off assertions from Mr. Simpson's lawyer, Gabriel Grasso, that several items Mr. Fromong had that day were once stolen from Mr. Simpson.

"Everything that was in that room was mine," said Mr. Fromong, insisting that he had canceled checks proving he bought the goods from another memorabilia dealer, Mike Gilbert.

Mr. Fromong was the first witness in what is expected to be a two-day hearing at which a judge will decide whether prosecutors have enough evidence to take Mr. Simpson and two co-defendants, Clarence Stewart and Charles Ehrlich, to trial on 12 charges including armed robbery and kidnapping.

Mr. Simpson, 60, has said he and five acquaintances entered the room at the Palace Station Hotel-Casino near the Las Vegas Strip to retrieve things that he contended were rightfully his. Among those items were several signed footballs and pictures, some plaques and three ties that Mr. Simpson was believed to have worn during the 1995 trial in which he was acquitted of charges he murdered his former wife and friend of hers.

Also taken in the raid were lithographs signed by another former N.F.L. star and baseballs signed "I'm sorry I bet on baseball" by the disgraced baseball great Pete Rose. Mr. Rose was banned from Major League Baseball for life in 1989 for wagering on his own team, the Cincinnati Reds.

Three other men who joined Mr. Simpson in raiding the room have accepted plea deals and are expected to testify about their involvement during this week's hearing. Two of those men have acknowledged having guns and said Mr. Simpson asked for guns to be present for the raid.

Mr. Fromong testified that he and a colleague, Alfred Beardsley, had been invited to the room by Thomas Riccio, a Los Angeles memorabilia dealer, who had told them he had a wealthy buyer interested in buying the Simpson items. Mr. Riccio is expected to testify this week as well.

Mr. Grasso, the lawyer for Mr. Simpson, worked to cast doubt on the ownership of the Simpson memorabilia in the room and to assert that Mr. Fromong had been trying to profit from the reported robbery by seeking a book or movie deal. Mr. Fromong acknowledged that he had considered such a project and hoped that the actor Jack Nicholson would play him in a film, but he said has not pursued this idea formally.

After Mr. Fromong's testimony, Mr. Riccio took the stand for two hours and testified that he arranged the hotel-room confrontation for Mr. Simpson after Mr. Beardsley contacted him to sell several Simpson items. He described how Mr. Simpson plotted the raid.

"I have my boys here; we're going to take care of it," Mr. Riccio recalled Mr. Simpson as saying.

He informed Mr. Simpson of the items that Mr. Beardsley said he had, and Mr. Riccio agreed to help organize a meeting if Mr. Simpson was willing to autograph several copies of a book published that week in which the ex-football star wrote about how he might have executed the 1994 slayings.

The book, "If I Did It," was written by Mr. Simpson as what he called a fictional account of how he would have killed his ex-wife, Nicole Brown Simpson, and her friend, Ronald Goldman. It was to be published in 2006 by HarperCollins before that plan was spiked in the face of public outrage.

A court then ordered that the Goldman family could publish the book and use the proceeds from its sales to pay down a $38.5 million civil judgment against Mr. Simpson. Mr. Simpson, found liable for the two deaths in a 1996 civil lawsuit, has disavowed the version of the book that the Goldmans published.

"O.J. told me, 'That's not my book anymore; I want nothing to do with it anymore,' " Mr. Riccio said. "So I said, 'Then sign it.' This is not my book." And he said, 'Oh, O.K.' "

The hearing on Thursday took on a y frenzied atmosphere similar to that of Sept. 19 when Mr. Simpson had a his bond hearing and was released after being held in county jail for three days. As with that incident, the courthouse steps featured such characters as a man in a chicken suit holding a sign proclaiming Mr. Simpson's guilt and a woman on roller skates in a rabbit costume that read, "Stop police brutality."

Inside, Mr. Simpson wore a gray suit and a broad smile as he limped into the courtroom, chatting amiably with friends and shaking reporters' hands during a break. He sat gnashing his teeth but largely silent as Mr. Fromong answered questions.

At the center of the courtroom pews was Marcia Clark, the prosecutor who failed to convict Mr. Simpson on double murder charges in 1995 and who is now a special correspondent for the television program "Entertainment Tonight."

More O.J. Pieces by Steve Friess