WASHINGTON -- Newly uncovered evidence in the terrorist bombing of a Pan American jumbo jet in December 1988 indicates for the first time that Libyan intelligence agents may have assembled and planted the bomb that destroyed the plane, U.S. government investigators involved in the inquiry said this week.
Until now the 2-year-old inquiry into the bombing over Lockerbie, Scotland, has focused on evidence that Iran hired a Syrian-sponsored terrorist group, the Popular Front for the Liberation of Palestine-General Command, to bomb a U.S. airliner in late 1988.
The accepted theory had been that a cell of the Popular Front based in West Germany assembled the bomb and smuggled it onto the aircraft.
U.S. officials, who spoke on condition of anonymity, stressed that the new evidence did not clear Iran, Syria or the Popular Front group of complicity in the Pan Am disaster.
They said they still believed that Iran commissioned the attack in revenge for the accidental downing of an Iranian passenger jet in July 1988 by a U.S. Navy warship in the Persian Gulf and that Syrian officials were aware of the Popular Front's activities and took no action to stop them.
But, they said, investigators now believe the Popular Front's leader, Ahmed Jabril, who is based in Damascus, paid agents of Libyan leader Col. Muammar el Kadafi to carry out the Pan Am bombing after discovering in October 1988 that Western intelligence agents had penetrated his own operations.
The evidence of a possible Libyan link, first reported publicly this week by the French news magazine L'Express, was confirmed and detailed by U.S. officials involved in the investigation of the Pan Am bombing.
In response to a question, officials said the disclosure was not intended to draw attention away from Syria's role in the bombing now that Syrian President Hafez el Assad has sent troops to Saudi Arabia and has joined the international opposition to Iraq's invasion of Kuwait.
The Boeing 747 jet was blown apart by a plastic explosive concealed in a radio cassette player on Dec. 21, 1988, as it flew 31,000 feet over Lockerbie.
The blast killed all 259 people on the plane, including 188 Americans, and 11 other people in the village of Lockerbie below.
Under Colonel Kadafi's rule, according to U.S. officials, Libya has been a leading sponsor of terrorism directed against the United States.
The new evidence, which is circumstantial, centers on the detonator for the Pan Am bomb, part of which has been recovered by Scottish workers who walked over 800 square miles of rural countryside looking for crash debris.
Scottish and American investigators have concluded that the recovered portion is identical to 10 timers that were seized from two Libyan intelligence agents in the West African nation of Senegal in February 1988, 10 months before the Pan Am bombing.
According to accounts in the French press in 1988 that were confirmed by U.S. officials, the Libyan detonators seized in Senegal differ fundamentally from those used by the Popular Front in West Germany.
The Popular Front detonators include both a timer and an altimeter, insuring that a bomb will not explode until after an aircraft has flown for a predetermined time at a specific altitude. The less sophisticated Libyan detonators have only a timer.
Investigators have said the bomb that destroyed the Pan Am jet was similar to bombs made by the Popular Front in that both employed aplastic explosive called Semtex and were concealed in Toshiba model radio-cassette players. But they have not disclosed the type of detonator used in the device.
Investigators are said to believe Libyan agents used Mr. Jabril's blueprint for the bombing, including much of the design for the bomb itself, but employed their own agents and bomb components.
"At least on the intelligence level, the case has now been made for Libyan participation in the destruction of Pan Am Flight 103," one official said.
"The timing device that was incorporated in the bomb that brought down 103 was of Libyan origin."
The officials called the Libyan evidence an important breakthrough in the Pan Am inquiry, which had appeared to stall in the last year. But they said much more work remained before investigators reach the legal standards of proof required to indict and arrest suspects.
Among other gaps in the case, experts have yet to reconstruct how a Libyan bomb was built and smuggled onto the Pan Am jet and to discover the identities of Libyan terrorists involved in the plot.
Secretary of Defense Dick Cheney and Secretary of State James A. Baker III were told of the new evidence in the last month, officials said.
The Scottish officials who head the Pan Am inquiry are holding a public hearing this month in Lockerbie to determine the physical cause of the accident.
The evidence of Libyan involvement, part of a separate criminal investigation conducted by the United States, Britain, Germany and other countries, has not been mentioned during the hearings.
The Libyans who were arrested in Dakar in 1988, identified only by their aliases as Mohammed Marzouk and Mansour Omran Saber, had left the Libyan Embassy in Benin and were on an Air Afrique flight to Abidjan, Ivory Coast, when they were arrested Feb. 20, during a layover in the Senegalese capital.
In their luggage, Dakar police found nine kilograms of Semtex plastic explosive, which is similar to that used in the Pan Am blast, several blocks of TNT and 10 timer-activated detonators.
United States officials said yesterday that Senegalese officials released the two Libyans on June 16, 1988, barely six months before the Pan Am bombing, over the protests of U.S. diplomats.