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Key events since the Lockerbie bombing:

Roy Letkey/AFP/Getty ImagesDec. 21, 1988 -- Pan Am Flight 103 from London to New York is destroyed over Lockerbie, Scotland, by plastic explosives hidden in a radio cassette player in the baggage compartment. All 259 passengers and crew are killed, as are 11 people on the ground.

May 1990 -- The Presidential Commission on Aviation Security and Terrorism, formed after the bombing, recommends a top-to-bottom overhaul of the U.S. aviation security system.

July 1990 -- The United Kingdom's Air Accidents Investigation Branch releases its formal investigation on the bombing, recommending that aircraft manufacturers study measures to mitigate the effects of a midair explosion.

November 1991 -- Two Libyan intelligence operatives are indicted for planting the bomb at an airport in Malta. But Libyan leader Moammar al-Gadhafi refuses to turn over the suspects.

April 1999 -- After years of negotiations and sanctions against Libya, the suspects are turned over for trial.

Abdel Basset Ali al-Megrahi (Wikimedia Commons)January 2001 -- One of the Libyan intelligence agents, Abdel Basset Ali al-Megrahi, is convicted of the bombing and sentenced to life in prison. A co-defendant was acquitted.

December 2002 -- After the installation of hundreds of explosives detection machines, 100 percent of checked bags are screened for explosives as a result of a congressional mandate passed after 9/11.

June 2007 -- A Scottish appeals commission rules that al-Megrahi "may have suffered a miscarriage of justice" and should be granted a new appeal.

November 2008 -- Families of the 180 American victims of Pan Am 103 receive final compensation from the Libyan government.