(NewsNation) — Richard Marquise wants answers. The retired FBI agent worked on the deadliest terror attack on British soil that has finally yielded a criminal capture more than three decades in the making.

On December 21, 1988, Pan Am Flight 103 fell from the sky. A bomb exploded midair, shortly after takeoff, killing all 259 passengers from 21 different countries on board, including 190 Americans. 11 more died on the ground in Lockerbie, Scotland.

“Clearly, it was a very significant attack against the world, against the United States. I recall there was something like 16 children under the age of 10 on that aircraft. It was an attack on all of us done by a state sponsor of terrorism,” Marquise said. “This was a very significant attack that took place long before we ever even though about a group like Al-Qaeda.”

More than 33 years later, the Justice Department announced Sunday that the Libyan intelligence official, who authorities say made the bomb that exploded on the flight, has been taken into American custody. Abu Agila Mohammad Mas’ud Kheir Al-Marimi will face federal charges in Washington, the Justice Department said.

Marquise says Mas’ud was on their radar during the investigation.

“We knew about an individual that had built the bomb, but he was never fully identified. It was not until Ken Dornstein, who lost a brother on the flight, put a lot of information together. With that, he went to Libya and conducted a great deal of investigation that led him to create a three-part series that played on PBS. During that investigation, he more fully identified Mas’ud. That information was passed to the FBI and to Scottish police,” Marquise said. “What happened today was a culmination of their added investigation.”

Marquise is hopeful that Mas’ud being in custody will be able to place a lot more pieces of the puzzle together.

“There’s no closure. There’s no high fives. It’s a very sad day for everyone, but I’m hopeful that he (Mas’ud) can at least tell us the rest of the story before we’re all too old to appreciate it or are no longer here, which unfortunately, is happening to many of the victims’ families as we all get older,” Marquise said.

Of the Americans on the Pan Am flight, 35 Syracuse University students were killed. They were returning home for Christmas after spending a semester abroad.

The university released a statement, saying in part: “Today’s news is a significant milestone in a decades long process to bring those responsible for the despicable act to justice.”

It’s justice that Bert Ammerman has been fighting for in remembrance of his 36-year-old brother, who was killed on the flight.

“My initial reaction was satisfaction. Then I shrugged a little bit and said, ‘again?’ Then most importantly, what’s next,” Ammerman said.

He added: “I personally believe strongly if we had handled the bombing of Pan Am Flight 103 appropriately in 1988 and 1989, we might not have had 9/11.”

Ammerman says while there’s no such thing as closure for him, Sunday’s announcement brings him one step further in his healing journey after losing his brother.

“He was just a good person. You hear that all the time when you talk about it. There were great people on that plane that didn’t live their full life. He was one of those,” Ammerman said. “He was one of the nicest human beings you could ever meet. He always wanted to make sure people were comfortable, people were happy. He’s the type of person that you wanted to see live a full life.”

Mas’ud is the third Libyan official charged in the U.S. linked to the Pan Am attack, but he would be the first to make an appearance in an American courtroom for prosecution in the case.

The Libyan government previously surrendered Abdel Baset Ali al-Megrahi and Lamen Khalifa Fhimah to a panel of Scottish judges sitting in the Netherlands. Al-Megrahi was convicted, but died after being released on humanitarian grounds in 2009 following a prostate cancer diagnosis. Fhimah was acquitted of all charges.

Mas’ud reportedly faces two criminal counts linked to the explosion. The initial announcement of charges against Mas’ud came in 2020, on the 32^nd anniversary of the bombing.

“I’d like him (Mas’ud) to confirm what we suspect that number one, he built a device. He’s told this to a Libyan police officer already in an interview about 10 years ago. But I would like to have him confirm that and confirm who else was involved. And then certainly if, in fact, he was involved in the actual planning, who were the other individuals who ordered this so that additional action could be taken against the other people who may still be alive,” Marquise said.

Officials have not shared how Mas’ud was taken into custody, but local Libyan media reported last month that he had been kidnapped from his residence in Tripoli. Following the incident, the foreign minister for the country’s Tripoli-based government told the BBC that they were “very open in terms of collaboration in this matter” when it came to extradition.

The Associated Press contributed to this report.