Amin Khalifa Fhimah also stood trial with Megrahi, but was acquitted of any involvement.
Last year, exactly 26 years on from the atrocity, the Lord Advocate led a delegation of Scottish law officers who attended a memorial at the Arlington cemetery in Washington.
Mr Mulholland, who addressed the service, said no Crown Office investigator or prosecutor has raised a concern about the evidence in the case and he vowed to track down Megrahi's accomplices.
He has previously said the idea that Megrahi had acted alone was "risible", and said "justice has only partly been done".
Megrahi's part in the bombing has been called into question in a series of books and documentaries.
A hearing will take place today to decide whether relatives of Lockerbie bombing victims could pursue an appeal on behalf of the only man convicted of the atrocity.
A group of British relatives maintain they have a "legitimate interest" in trying to get the case of Abdelbaset al-Megrahi back before a court for a full appeal.
They believe the Libyan, who died protesting his innocence in his home country in 2012, was the victim of a miscarriage of justice and say his conviction should be overturned.
The Scottish Criminal Cases Review Commission (SCCRC), which is once again looking at Megrahi's conviction, has petitioned the High Court asking for guidance on whether members of the victims' families can take forward such an appeal on the convicted man's behalf.
A hearing on the issue will take place before three judges at the Appeal Court in Edinburgh today.
Megrahi was found guilty of the bombing of Pan Am flight 103 over the south of Scotland on December 21 1988 in which 270 people were killed.
He died after abandoning his second appeal, which itself came after the SCCRC referred the case back to senior High Court judges in 2007.
Since June last year, the SCCRC has been considering a fresh, joint application from members of Megrahi's family and the Justice for Megrahi campaign group, which includes relatives of British victims of the bombing, to review the conviction.
Aamer Anwar, solicitor for the Megrahi family and 26 relatives of Lockerbie victims, said:
Representatives of some of those killed in the Lockerbie bombing are challenging the conviction of the man found guilty of blowing up the flight.
Libyan Abdelbaset al-Megrahi was convicted of causing the deaths of the 270 people killed in the attack on Pan-Am Flight 107, which happened in 1988.
But some of the families believe he was innocent, and have been at the High Court in Edinburgh to pursue an appeal against his conviction.
Al-Megrahi died three years ago and the court is being asked to decide if legal proceedings could continue without his family's involvement.
Campaigners who believe the Lockerbie bomber Abdelbaset Al Megrahi didn't get a fair trial have met the man in charge of the investigation.
Members of the Justice for Megrahi campaign want to reopen the inquiry into Megrahi's conviction.
They think that many aspects of the orginal investigation were mishandled and want the former chief constable of Dumfries and Galloway Police Pat Shearer to look into their allegations.
Matthew Taylor has this report:
Campaigners who believe the Lockerbie bomber Al Megrahi didn't get a fair trial are to meet with the man in charge of the investigation.
Former chief constable of Dumfries and Galloway Police Pat Shearer will speak to members of the Justice for Megrahi campaign in Dumfries today.
Scotland's First Minister, Alex Salmond has given this reaction to the death of Abdelbaset al-Megrahi.
The father of one of the victims of the Lockerbie bombing says he is 95% convinced that Abdelbaset al-Megrahi was not responsible.
He added that an "enormous red herring' has been removed, and now he can press for an independent inquiry into why the bombing was allowed to happen.
Former Lockerbie councillor Marjory McQueen was an eyewitness on the night on the bombing.
She says she thinks no one will ever know the truth surrounding exactly who was responsible for the deaths of 270 people on 21 December 1988.
Abdelbaset al-Megrahi's sister has told the Libyan Wal news agency that his funeral will take place at Tripoli's main cemetery on Monday, following early afternoon prayers
The Leader of the Scottish Liberal Democrats has commented following reports that al-Megrahi has died at home in Libya, after a long battle with cancer.
Abdelbaset al-Megrahi, 59, was sentenced to life in prison for the 1988 bombing of a US airliner which claimed 270 lives.