Camp Zeist, Netherlands ? New witnesses told the Lockerbie appeals court Wednesday that they saw evidence of a break-in at a restricted baggage area of Heathrow Airport the same day that a bomb exploded on board a Pan Am flight in 1988, killing 270 people.

Defense attorneys for the Libyan convicted of the bombing, Abdel Basset Ali al-Megrahi, say the testimony by two Heathrow security guards cast doubt on the verdict, which should be quashed.

Al-Megrahi, a former Libyan intelligence agent, was sentenced a year ago to life in prison after the trial court found he had put the bomb into the international baggage system as unaccompanied luggage in Malta.

Last week, defense attorney William Taylor told the appeals court that the new evidence would support defense claims that the bomb was more likely to have been loaded on the plane in London than in Malta.

Raymond Manly, a retired security guard at Heathrow, said he discovered the break-in about 18 hours before the doomed New York-bound airliner took off. Manly’s supervisor, Philip Radley, confirmed Manly had reported the incident to him and that the police were informed.

The bomb, which police said was concealed in a cassette-recorder inside a brown suitcase, destroyed Pan Am Flight 103 on Dec. 21, 1988, killing all 259 people on board and 11 on the ground in the Scottish town of Lockerbie.

Manly described the padlock on the access door to the baggage area as a U-shaped piece that was secured between two doors by a 1-inch-thick metal bar. He said he found the “bar out of position,” leaving easy access to the restricted area.

Manly said it looked like a “very deliberate act” by professionals.

Radley recorded the incident in his logbook with the words “Door at T3 2a lock broken off.”

“I thought it was snapped off with great force,” Radley said. “The arm was broken.”

Prosecution witnesses said the door could have been forced open by a baggage handler or guard taking a shortcut to leave a restricted area, and that there was no break-in.

Geoffrey Myers, who took over Radley’s shift on Dec. 21, said he had seen similar damage frequently before.

Under cross-examination, Manly flared in anger when deputy prosecutor Alan Turnbull questioned his memory when he failed to locate the forced door on a map.

“This is not a comedy house. It’s very, very serious,” he said. “I suffered, and I’m suffering still. I lived with this for 13 years, and if it would have been acted upon, we would not be sitting here.”

Radley and Manly were never called to testify in the original trial. The defense said it had no knowledge of this evidence until after the verdict was delivered last Jan. 31.

The prosecution had tried to block the appearance of the new witnesses, saying the overwhelming circumstantial evidence on which al-Megrahi was found guilty remained valid. It asked the court to uphold the conviction.

The prosecution’s case, accepted by the trial court, rested on the testimony of a Maltese shopkeeper that al-Megrahi purchased clothing at his store that police identified as the items used to pad the bomb inside the suitcase.