The cockpit recording from the hijacked aeroplane which crashed in Pennsylvania on 11 September 2001 can be played in a courtroom, a US judge has ruled.
Flight 93 crashed in Pennsylvania killing 40 passengers and crew
It is unclear whether the tape - which has so far only been played to victims' relatives - will be publicly released.
It will be played in the sentencing trial of Zacarias Moussaoui - the only man tried in the US in connection with 9/11 - which reconvenes on Thursday.
The jury has said he can be executed - now it must decide whether he should.
The 37-year-old French citizen has pleaded guilty to six counts of conspiracy to attack the US.
The defence is expected to argue that Moussaoui - who has admitted to being a member of al-Qaeda - suffers from mental illness and had a difficult childhood.
Prosecutors are said to be planning to read out the names of the 2,972 victims of the attacks, and show their pictures in court.
It is also reported they will present Rudy Giuliani, who was New York mayor at the time of the attacks, as a witness.
On the eve of the trial's resumption, Judge Leonie Brinkema ruled that the cockpit tape could be played to the court. But she gave relatives of the Flight 93 victims until Tuesday to request the audio be kept from the general public.
Judge Brinkema said she was aware that relatives might object "to the voices of their loved ones being publicly revealed in this manner".
But she said that if there were no objections, the recording would be released to the public the day after it was submitted as evidence.
The commission set up to investigate the 9/11 attacks described the final minutes of the flight in its report and released some details of what was heard on the cockpit recording.
Prosecutors want to use the recording to show the jury how passengers were treated by 9/11 hijackers.
Flight 93 was one of four planes hijacked on 11 September 2001. En route from New Jersey to California, it crashed in Shanksville, Pennsylvania, killing 40 passengers and crew.
Mobile phone conversations from passengers and flight attendants showed that they had heard about the other hijackings and planned to fight back.
It is thought that hijackers crashed the plane, believed to be heading for Washington, when passengers were close to overwhelming them.