An FBI expert testified via videotape Wednesday in O.J. Simpson's armed robbery trial that it's impossible to tell whether an audio tape of the hotel room confrontation was altered, but the judge said she still might let jurors hear the recording.

FBI forensics audio examiner Kenneth Marr said in prerecorded testimony that the tiny digital recorder secretly used by collectibles broker Thomas Riccio to record the alleged robbery last year didn't have advanced features that would ensure the security of the information on it.

But Marr did authenticate another tape that Riccio said he obtained with a separate analog recorder at a pool at the Palms hotel and casino. That recording was made several hours before the conflict between the former football star and two sports memorabilia dealers at the Palace Station hotel.

Prosecutors say the analog tape includes the voices of Simpson and several other men planning to confront the memorabilia peddlers, Bruce Fromong and Alfred Beardsley.

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Marr's appearance was videotaped Aug. 25 because he was scheduled to be out of the country. Asked by Clark County District Judge Jackie Glass if he could say whether the digital recording contained edits or manipulations, Marr replied: "I could not determine if those files had been altered or not."

A key question is whether any of the tapes contain mention of guns being used. Both Simpson and co-defendant Clarence "C.J." Stewart say they saw no guns.

Stewart's defense lawyer, Brent Bryson, lost a bid to have both recordings disqualified as evidence because of problems including who had custody of them. The digital recorder was kept from police for eight days while Riccio sold the tape to an Internet gossip site.

"The device itself is inherently untrustworthy," Bryson said.

Glass said she would allow the poolside recording and let the recording from the hotel room be used if the voices on the tape could be individually verified.

Simpson and Stewart have pleaded not guilty to 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 maintains that he was trying to retrieve personal items that had been stolen from him.

The former NFL star 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 him liable for $33.5 million in damages.