U.S. District Judge Leonie Brinkema limited the scope of Rolince's testimony after the defense objected that he was trying to describe what the FBI would have done if it had known about Moussaoui's terrorist ties.
The defense argued that speculative testimony based on a hypothetical confession by Moussaoui unfairly implied that Moussaoui had some obligation to confess.
Brinkema allowed some limited hypothetical questioning but advised the jury: "Juries cannot decide cases on speculation. ... Nobody knows what would have happened."
Zacarias Moussaoui pleaded guilty Friday to conspiring with the hijackers in the Sept. 11 plot and declared Osama bin Laden personally instructed him to fly an airliner into the White House.
A British man whose behavior raised suspicions at a flight school in the southern state of Georgia has been located in England, an FBI official said Friday.
District Judge Leonie Brinkema said the jury considering whether to execute Moussaoui could hear the recording from United Airlines Flight 93 and see a transcript of it.
Luggage that didn't get put on hijacked jet provided information about terrorists, say former investigators.