But the spy, identified by the pseudonym "Abdul Majid Giaka," added new pieces of circumstantial evidence against two Libyan intelligence agents accused in the December 1988 bombing.
The witness appeared on the stand after nine years of hiding in the U.S. witness protection program. Only the people in the courtroom could see or hear him. Video images broadcast to the public gallery were blocked and his voice was distorted to keep his identity secret.
The defendants, Abdel Basset Ali al-Megrahi and Lamen Khalifa Fhimah, are charged with murder and conspiracy to murder the 259 passengers killed aboard the Boeing 747 and the 11 others who died on the ground in the Scottish town of Lockerbie.
Testifying on the 50th day of hearings since the trial opened May 3, Giaka said he worked in Malta since 1986 for the Libyan intelligence, Jamahriya Security Organization, using his job as the assistant station manager for Libyan Arab Airlines as a cover.
Fhimah was his immediate boss and Megrahi was a senior intelligence officer previously in charge of airline security.
Giaka said Fhimah kept bricks of explosives locked in desk drawers at Malta airport for two years, until just a few weeks before the bombing. He also said he saw Megrahi with a "brownish" suitcase similar to the one the indictment says contained the bomb that blew up the airliner.
But in four hours of testimony in Arabic, Giaka drew no connection between the explosives he saw at the Libyan airlines office and the suitcase Megrahi allegedly carried to the bombing of Pan Am 103.
Giaka was unclear about the timing of several key incidents, including the date he saw Megrahi arrive in Malta and collect a hard-shelled "shiny brownish" Samsonite-like suitcase from the baggage carousel the same kind the prosecution says concealed the Lockerbie bomb.
Giaka said it was "two or three weeks" after an earlier trip by Megrahi on Dec. 7, 1988, and Fhimah was there to greet him. The Lockerbie bomb exploded Dec. 21.
Giaka claimed he reported Megrahi's arrival in his regular contacts with the CIA. But prosecutor Alastair Campbell indicated the report was not among the dozens of cables that the U.S. agency declassified and handed over to the court.
Asked how he would respond if the CIA denied hearing about the incident, Giaka said, "I don't think they would be telling the truth."
Giaka said he became a CIA agent in August 1988 because he was "uncomfortable" with his organization's "involvement in terrorism and the way it handled dissidents" against the regime of Libyan strongman Moammar Gadhafi.
But Giaka also admitted he was afraid of losing his intelligence joband the exemption from military service because of an incident at the airport involving an Egyptian teen-age girl's complaint of sexual harassment.
Initially he wanted help to flee to the United States, but agreed to stay and spy for the CIA, which paid him $1,000 per month and helped him get bogus surgery to avoid military service.
By ARTHUR MAX