LONDON – U.S. prosecutors are expected to unseal new charges next week against another suspect in the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, that killed 270 people, the majority of them Americans, a person familiar with the matter said Thursday. 

Abu Agila Mohammad Masud, a Libyan intelligence officer, is suspected of helping to make the bomb that exploded aboard the Boeing 747 while it was flying over the small Scottish town en route from London to New York, said the person, who is not authorized to comment publicly.  

The expected charges would represent a fresh chapter in one of the world’s longest and most sprawling terrorism investigations. Investigators have pursued leads in dozens of countries and interviewed thousands of people in connection with the incident.

For Attorney General William Barr, who is leaving office next week, the case also has been a deeply personal one. During his initial stint as attorney general in the George H.W. Bush administration, Barr announced the first charges in the case aided by Robert Mueller, then chief of the Justice Department’s Criminal Division.

“This investigation is by no means over,” Barr said while unveiling the initial charges in a 1991 briefing. “It continues unabated.”  

The Wall Street Journal first reported the development in a case that remains the deadliest terrorist attack to take place on British soil. 

In addition to the 259 people killed aboard the flight less than an hour after takeoff, 11 people on the ground were killed as the plane’s wreckage scattered for miles. 

Masud is believed to be in custody in Libya. The U.S. is expected to seek his extradition.

In 2001, Libyan intelligence officer Abdel Basset Ali al-Megrahi became the only person convicted for the attack. He was given a life jail sentence. However, authorities in Scotland released him in 2009 on humanitarian grounds after he was diagnosed with prostate cancer. He later died at his home in Libya’s capital, Tripoli, at age 60. 

The Obama administration opposed the move. 

Megrahi maintained he was innocent. At the time of the bombing, he was officially serving as chief of security for the state-owned Libyan Arab Airlines. But prosecutors argued that was just a front for his role as a security officer for Jamahiriya Security Organization, Libya’s intelligence branch under then-leader Moammar Gadhafi. 

Megrahi’s connection to the bombing was established only after investigators discovered a tiny plastic fragment and the remains of a shirt amid the debris. The plastic was determined to be part of the timing device that detonated the bomb. The shirt was packed inside the suitcase. A shop owner testified that Megrahi bought the shirt from her.