The former head of the FBI believes more people will be charged over the Lockerbie bombing.
Robert Mueller, who finished a 12-year spell as FBI director in September, said progress has been made in the investigation since the Libyan revolution in 2011.
Abdelbaset al-Megrahi is the only person to have been convicted of the bombing of Pan Am flight 103 over Scotland in which 270 people were killed on December 21 1988, nearly 25 years ago.
Megrahi, who was released from jail by the Scottish government on compassionate grounds after being diagnosed with prostate cancer, died last year protesting his innocence.
Since the fall of the Gaddafi regime, British and US investigators have been working to establish if there are other individuals in Libya who could be brought to trial for their involvement in the attack.
Speaking in a BBC documentary in the lead up to the 25th anniversary of the bombing Mr Mueller said he was confident that the ongoing investigation would “produce results”.
He said: “We have FBI agents who are working full-time to track down every lead as we have since it occurred 25 years ago.
“My expectation is that continuously we will obtain additional information, perhaps additional witnesses and that others will be charged with their participation in this.
“We do not forget. And by that I mean the FBI, the Department of Justice, we do not forget.”
It comes as Scotland’s Lord Advocate announced that Libya has appointed two prosecutors to work on the investigation into the bombing.
Frank Mulholland said it was a “very welcome development” which he hoped “will bear fruit and result in bringing others to justice”.
A series of events in Lockerbie, London and Washington are planned for Saturday, the 25th anniversary of the disaster, to remember the 270 people that died.