(Credit: Win McNamee/Getty Images)

ARLINGTON, Va. - Memorial services were held today at Arlington National Cemetery in remembrance of the 270 people killed in the 1988 Pan Am flight 103 bombing, one of several occurring simultaneously in the U.S. and United Kingdom this weekend to observe the 25th anniversary of the tragic flight from London to New York.

"Although a quarter century has passed since the world was shaken - and so many lives were devastated - by a heinous and cowardly act of terror, no amount of distance or time can ease the pain, or erase the loss, that was inflicted on that day," Attorney General Eric Holder told family and friends of the victims. "Even now, it remains difficult to comprehend the magnitude of such a senseless crime, which claimed the lives of 259 innocent men, women, and children in the skies above Scotland, along with the lives of 11 residents of the peaceful town of Lockerbie."

Several hundred turned out for the quiet ceremony, which included a procession from the United Kingdom featuring officials directly affected by the terror attack. The attorney general thanked "the tremendous generosity" of the Scottish people.

"Particularly the people of Lockerbie, who, despite their own losses, opened their homes to the families of victims who streamed into that small town from around the world in the days after the bombing," he said. "In the midst of their anguish, these generous men and women gave what comfort they could offer, and shared what solace they could provide."

The event today was organized by the family group Victims of Pan Am Flight 103. Services included a bagpipe rendition of "Amazing Grace," choir song, and a wreath-laying at the base of the cemetery's Lockerbie monument. Each of the victims' names were solemnly read.

Holder also acknowledged the efforts of the families as well as current and former and law enforcement officers who "selflessly defined the quest for justice in the aftermath of this crime as their life's work."

Only one man was eventually convicted of the bombing by a Scottish court in 2001: former Libyan intelligence officer Abdelbaset al-Megrahi. He was later freed on humanitarian grounds in 2009, over the protest of the U.S. government, when it was revealed he was in the later stages of prostate cancer. He died at his home in Tripoli in 2012.

Officials in both the the U.S. and U.K. have openly suggested the attack may have been an act of state-sponsored terrorism, but the truth may never be known.

The governments of both countries issued a joint statement today regarding those unanswered questions.

"We are striving to further deepen our co-operation and welcome the visit by U.K. and U.S. investigators to Libya in the near future to discuss all aspects of that co-operation, including sharing of information and documents and access to witnesses," it read.

TSA administrator John Pistole and former FBI director Robert Mueller, who was one of the original legal team that sought to indict al-Megrahi, both spoke in Arlington. British ambassador Peter Westmacott and Scottish Undersecretary of State David Mundell also gave remarks, including the reading of a written statement from British Prime Minister David Cameron.