The recording of OJ Simpson storming into a Las Vegas hotel room during an alleged armed robbery could not be authenticated, an FBI examiner said.

Kenneth Marr, an audio examiner with the FBI, told the jury it was "not feasible" to confirm whether or not the digital recording had been manipulated in any way.

The audio recording was taken as Simpson and five other men, two of whom were armed, allegedly stormed into a room at the Palace Station Hotel in Las Vegas and took between 700 and 800 items related to his sporting career on September 13 last year.

Simpson again faces life in prison if convicted of the kidnapping and armed robbery charges in his trial at the Regional Justice Centre in Las Vegas, 13 years after he was acquitted of murder in the televised "trial of the century" in Los Angeles.

Simpson's high-profile 1994 trial saw him cleared of murdering his wife Nicole Brown Simpson and her friend, Ronald Goldman, in a verdict which shocked many in the United States.

In Las Vegas, prosecutors have said the recording caught the entire six-minute incident and included the former American football star shouting obscenities in the so-called "sting" on two memorabilia dealers in room 1203 of the hotel.

Simpson, 61, and his co-defendant Clarence "CJ" Simpson, 54, deny 12 charges, including kidnapping, armed robbery, and assault. The trial continues today.