WASHINGTON — Attorney General William P. Barr on Monday announced criminal charges against a former Libyan intelligence operative accused of building the explosive device that was used in the 1988 bombing of Pan Am Flight 103, one of the deadliest terrorist attacks in United States history, stemming partly to a confession that he gave nearly a decade ago while imprisoned in Libya.
The announcement bookends Mr. Barr’s two tours of duty as attorney general, first under President George Bush and now under President Trump. At his first news conference as the acting attorney general under Mr. Bush in 1991, he announced charges against two suspects in the explosion of the jetliner over Lockerbie, Scotland. On Monday, the 32nd anniversary of the attack, Mr. Barr revealed charges against a third person, a shadowy bomb expert named Abu Agila Mohammad Mas’ud.
The Justice Department charged Mr. Mas’ud with two criminal counts, including destruction of an aircraft resulting in death, according to court documents unsealed on Monday. He is halfway through a 10-year sentence in a Libyan prison for unrelated crimes.
“Let there be no mistake,” Mr. Barr said. “No amount of time or distance will stop the United States, and its partners in Scotland, from pursuing justice in this case.”
Mr. Mas’ud’s name had surfaced during the investigation into the bombing of the flight, which killed 270 passengers, including 190 Americans. But officials examining what happened failed to confirm his identity or locate him after the attack, Mr. Barr said. Mr. Mas’ud appeared to have had a role in the explosion, but his exact involvement remained murky. But the department said that Col. Muammar el-Qaddafi, Libya’s leader at the time, personally thanked Mr. Mas’ud for carrying out the deadly operation and called it a total success.
After Colonel el-Qaddafi’s government collapsed, Mr. Mas’ud confessed to the bombing in 2012 while being interviewed by a Libyan law enforcement official. Investigators eventually learned about his detention and confession, Mr. Barr said, calling the development a “breakthrough.”
The attorney general, who steps down on Wednesday, said he was hopeful that the Libyans would extradite Mr. Mas’ud to the United States and called the prospects “very good.”
“Mas’ud is in the custody of the current government of Libya, and we have no reason to think that that government is interested in associating itself with this heinous act of terrorism,” Mr. Barr said. “We are optimistic they will turn him over to face justice.”
Extradition would allow Mr. Mas’ud to stand trial, but defense lawyers raised doubts about whether a confession obtained in prison in war-torn Libya would be admissible as evidence.
Mr. Mas’ud was the third suspect charged in the Pan Am 103 case. The other two, Abdel Basset Ali al-Megrahi and Al-Amin Khalifa Fhimah, were initially charged in 1991, but American efforts to bring them to justice were stymied when Libya refused to extradite them to either the United States or Britain for trial.
The Libyan government ultimately agreed to let them stand trial in the Netherlands under Scottish law, where Mr. Fhimah was acquitted and Mr. al-Megrahi was convicted in 2001 and sentenced to life in prison.
Scottish officials granted Mr. al-Megrahi a compassionate release in 2009 because he had cancer, a decision that angered the families of the victims and the United States government, including President Barack Obama. Mr. al-Megrahi died in 2012; his family posthumously appealed his conviction in Scotland. The request is pending.
Current and former American and Libyan officials said that Mr. Mas’ud was born in Tunisia in 1951 and at some point moved to Tripoli, Libya, and became a citizen. He worked for the Libyan intelligence service from 1973 to 2011, building bombs, and rose to the rank of colonel, according to court documents. After Colonel el-Qaddafi’s fall in 2011, Mr. Mas’ud was arrested and imprisoned in Misurata, Libya, before being moved to Al-Hadba prison in Tripoli.
Along with 38 other defendants, including one of Colonel el-Qaddafi’s sons and other former Libyan officials, Mr. Mas’ud stood trial on criminal charges related to the Qaddafi government’s efforts to quell the Libyan revolution.
The F.B.I. said it first received a copy of Mas’ud’s confession with the Libyan law enforcement officer in about 2017 and sought more information. The F.B.I. interviewed the Libyan law enforcement official this year and learned that he had taken the confession from Mr. Mas’ud in September 2012.
Court documents said that the official had questioned Mr. Mas’ud to determine whether he had “committed any crimes against Libya and the Libyan people during the 2011 revolution” in an attempt to keep Colonel el-Qaddafi in power.
Michael R. Sherwin, the acting United States attorney for the District of Columbia, described the circumstantial evidence as “extremely compelling” and pointed to travel records implicating Mr. Mas’ud, Mr. al-Megrahi and Mr. Fhimah.
In particular, the men had traveled to Malta before the attack, where investigators determined that the bomb had been placed inside a portable cassette player put aboard a plane and transferred twice before reaching Flight 103. On the day of the bombing, the complaint said, Mr. al-Megrahi and Mr. Mas’ud traveled from Malta to Tripoli on the same flight.
Mr. Mas’ud said in his confession that he went to Malta with the suitcase that contained the bomb and later set the timer for it to blow up exactly 11 hours later. According to the confession, Mr. Mas’ud worked with Mr. al-Megrahi and Mr. Fhimah to “execute the plot.”
“He explained that he hid the detonator and timer in a technical way that would make it difficult to be discovered, by placing it close to the metallic parts of the suitcase,” according to the confession. Mr. Mas’ud said “that he used approximately 1.5 kilograms of plastic Semtex, and he added that plastic explosives do not show up on the airport baggage scanner.”
The circumstances surrounding Mr. Mas’ud’s confession in prison in Libya were not clear. The court documents provide no further detail about the Libyan law enforcement officer or for whom he worked, but he said he would be willing to testify at a trial.
If Mr. Mas’ud were ever brought to Washington, defense lawyers would almost certainly seek to challenge the confession and argue it could have been coerced or tainted.
A 2017 United Nations report that mentions Mr. Mas’ud raises troubling questions about the treatment of former Libyan officials who were held at various prisons and put on trial after Colonel el-Qaddafi was overthrown.
“Many of the defendants were held in prolonged incommunicado detention, without access to their families or lawyers, and often in isolation, including at unofficial detention facilities, amidst allegations of torture and other ill treatment,” the report says.
Mr. Mas’ud’s suspected role in the Lockerbie bombing received new scrutiny in a three-part documentary on “Frontline” on PBS in 2015. The series was written and produced by Ken Dornstein, whose brother was killed in the attack. As part of his investigation, Mr. Dornstein learned that Mr. Mas’ud was being held in a Libyan prison and even obtained pictures of him.
In an email, Mr. Dornstein questioned the breakthrough that Mr. Barr had discussed. “For all of the talk of an ongoing investigation over the last few decades, I found surprisingly little new detail in the charging documents outside of the alleged confession,” he said.
Mr. Dornstein had also reviewed documents and interviews that connected Mr. Mas’ud to the bombing of the La Belle discothèque in West Berlin in 1986 that killed two American soldiers. According to his confession, Mr. Mas’ud also admitted to building the explosive used in that attack when he was questioned in 2012.