Libyan Abdel Basset al-Megrahi launched a second appeal today to try to reverse his conviction for the 1988 bombing of a US airliner over the Scottish town of Lockerbie, killing 270 people.
The appeal opened at Edinburgh's High Court before a panel of five judges.
Megrahi, 56, who is terminally ill with prostate cancer in Greenock prison near Glasgow, was not in court.
Defence lawyer Margaret Scott said the court proceedings were being relayed to Megrahi in prison, where he was undergoing "a new course of treatment" for his cancer.
The initial session is expected to last about a month, although some questions about the appeal process have been raised by the imminent ratification of a prisoner transfer agreement (PTA) between the UK and Libya.
The PTA, which was drawn up in 2007 but must be ratified by Britain and Libya before it can come into force, sets a framework for an application for Megrahi, a former Libyan agent.
A justice ministry spokesman told Reuters in London that ratification would take place "shortly". He added that in the case of prisoners in Scottish jails, including Megrahi, "any decision to transfer under this agreement would be for Scottish ministers and Scottish ministers alone".
Scotland has its own legal system separate from the rest of the UK. Legal sources said the appeal could only be terminated if Megrahi himself requested this.
Megrahi was sentenced to life imprisonment by a special Scottish court sitting in The Netherlands in 2001 and his initial appeal was turned down the following year.
The Scottish Criminal Cases Review Commission referred the case back to the High Court in June 2007 on the grounds Megrahi might have been the victim of a miscarriage of justice.
The Pan Am jumbo jet exploded over Lockerbie on route from London to New York on 18 December, 1988. Of the 259 people on board, 189 were Americans. Another 11 people were killed on the ground.
In 2003, Libya agreed to pay about £1.48bn to families of victims in a move that helped Tripoli's international rehabilitation after it had long been regarded by Western nations as a pariah state.
A number of procedural hearings have been held since the case was referred back to the High Court. These included a UK government demand that certain documents - believed to be related to the timer in the bomb - be kept secret from defence lawyers and the public for reasons of national security.
Megrahi's wife and some of his family have been living in a house in Glasgow rented by the Libyan government.