LAS VEGAS — Testimony resumed Wednesday in O.J. Simpson’s armed robbery and kidnapping trial with a videotaped appearance by an FBI audio analyst who prosecutors hope can authenticate recordings made by a key player still waiting to testify.
Simpson stopped and smiled at a man who shouted, ‘‘Stay out of trouble,’’ as the former football star arrived at court for a third day of testimony on charges over his alleged grab for sports memorabilia in a Las Vegas hotel room.
The charges could land him and a co-defendant, Clarence ‘‘C.J.’’ Stewart, in prison.
Robert Lucherini, a lawyer for Stewart, has already challenged the conclusions of FBI audio examiner Kenneth Marr, whose testimony began Tuesday via videotape about enhancing recordings made by collectibles broker Thomas Riccio.
Lucherini said in documents filed this month with the Nevada Supreme Court that Marr, whose testimony was taken Aug. 25, could not authenticate the recordings.
Riccio is waiting in a downtown Las Vegas hotel to testify about arranging the meeting between Simpson, Stewart and two memorabilia dealers a year ago.
‘‘They told me, ’Anytime from late Tuesday to early Thursday,’’’ Riccio told The Associated Press by telephone Tuesday. He said prosecutors told him to expect to be on the stand for as long as a day and a half and also asked him to ‘‘refrain from talking before I testify.’’
‘‘I hope they don’t just have to go by what I say,’’ added Riccio, who said he gave authorities more than 10 hours of audio recorded before, during and after the Sept. 13, 2007, alleged armed robbery. ‘‘All they have to do is listen to my tapes.’’
On Tuesday, surveillance experts from the Palace Station and Palms hotels in Las Vegas provided testimony about videos showing the comings and goings of Simpson; the five men who accompanied him; Riccio; and memorabilia dealers Bruce Fromong and Alfred Beardsley.
Prosecutors also called another FBI forensic audio analyst who said he downloaded digital recordings of the confrontation.
The jury already has heard snippets of recordings made by Riccio, 45, who set up the meeting and received immunity from prosecution.
Riccio, who sold recordings to a celebrity gossip Web site before police obtained them, testified at a November hearing that he saw a gun in the room, but that he wasn’t sure Simpson saw a gun.
Simpson has maintained that no guns were used, and that he wanted only to retrieve personal belongings from Fromong and Beardsley.
Simpson and Stewart are being tried on 12 charges, including armed robbery, kidnapping, assault with a deadly weapon and coercion. A kidnapping conviction could result in a sentence of life in prison with the possibility of parole. An armed robbery conviction could mean mandatory prison time.
Simpson escaped prison time in the 1990s after his acquittal in Los Angeles on charges of murdering ex-wife Nicole Brown Simpson and her friend Ron Goldman. A civil jury later found Simpson liable for $33.5 million in damages.
Riccio’s lawyer, Stanley Lieber, said he expected Riccio’s testimony would draw contentious challenges from the defense.
‘‘He’s got a past. They’ll play that up,’’ Lieber said.
Lieber said he did not know whether Riccio gained many takers for his promises to mention commercial products, restaurants and services while the spotlight is on him at the Simpson trial.
The lawyer said Riccio turned down a lifetime membership at a strip club and a sponsorship deal with a poker Web site.
Riccio also published a book last April that he touted as an inside account of events leading to Simpson’s arrest.
AP Special Correspondent Linda Deutsch contributed to this report.