The US Justice Department has unsealed charges against an alleged Libyan bombmaker over the 1988 explosion of Pan Am Flight 103 over Lockerbie, Scotland.

The attack killed 259 people in the air and an additional 11 on the ground.

The charges were announced on the 32nd anniversary of the bombing and in the final news conference of US attorney general William Barr’s tenure, underscoring his personal attachment to a case that unfolded during his first stint at the Justice Department.

He announced an earlier set of charges against two Libyan intelligence officials in his capacity as acting attorney general nearly 30 years ago, vowing that the investigation would continue.

Attorney general William Barr speaks during a news conference at the Justice Department in Washington
US attorney general William Barr at the Justice Department in Washington (Michael Reynolds/Pool via AP)

Though Mr Barr had not appeared at a press conference in months, he led this one two days before his departure as something of a career bookend.

In presenting new charges, the Justice Department is revisiting a case that deepened the chasm between the US and Libya, laid bare the threat of international terrorism more than a decade before the September 11 attacks and produced global investigations and punishing sanctions.

The case against the alleged bombmaker, Abu Agela Masud Kheir Al-Marimi, is right now more theoretical than practical since Masud is not yet in US custody, but it is nonetheless one of the more consequential counterterrorism prosecutions brought by the Trump administration Justice Department.

A breakthrough in the investigation came in 2016 when US officials learned that Masud was in Libyan custody after the collapse of the regime of Colonel Muammar Gaddafi.

In an interview that Masud gave to Libyan law enforcement several years earlier, US officials said, Masud admitted building the bomb in the Pan Am attack and working with the two other defendants to carry out the plot.

In 1992, the UN Security Council imposed arms sales and air travel sanctions against Libya to prod Gaddafi into surrendering the two suspects.

But the Libyan government baulked at surrendering the men to the US, sceptical they could receive a fair trial.

Libya ultimately turned them over for prosecution before a panel of Scottish judges sitting in a Netherlands court.

One man – former Libyan intelligence official Abdelbaset al-Megrahi – was convicted, and a second Libyan suspect was acquitted of all charges.

Abdelbaset al-Megrahi
Abdelbaset al-Megrahi (Danny Lawson/AP)

Megrahi was given a life sentence, but Scottish authorities released him on humanitarian grounds in 2009 when he was diagnosed with prostate cancer.

He later died in Tripoli.

The Pan Am flight exploded over Lockerbie less than an hour after take-off from London on December 21 1988, en route to New York City and then Detroit.

Among the Americans on board were 35 Syracuse University students flying home for Christmas after a term abroad.

The attack was the latest flare of tension between Libya and Western nations, including the US.

In the years before the flight, for instance, Libya was blamed for the bombing of a West Berlin discotheque that killed two American soldiers and injured dozens of others.

It was not until 2003 that Gaddafi and Libya accepted responsibility for the Pan Am disaster, with the country formally taking blame and reaching a 2.7 billion dollar compensation deal with the victims’ families.

Sanctions were lifted and, in 2006, the Bush administration removed Libya from its list of state sponsors of terrorism and restored diplomatic relations with the country.

Besides Mr Barr, another key figure in the Lockerbie investigation was Robert Mueller, who was the Justice Department’s criminal chief at the time the first set of charges was announced.

Mr Mueller would later become FBI director and special counsel in charge of the investigation into ties between Russia and the 2016 Trump campaign.