Lockerbie bombing: A timeline

In more than two decades since the Lockerbie bombing, families of the 270 victims of the disaster are yet to receive clear answers as to who was responsible.

Here is a timeline of key events:

• December 1988: 270 killed as plane explodes over Lockerbie

Pan Am flight 103, travelling from London to Detroit, explodes over the Scottish town of Lockerbie on 21 December.

All 243 passengers and 16 crew are killed after a bomb exploded on board, while 11 more people are killed as sections of the plane land on the ground.

• November 1991: Two men indicted over terror attack

Scottish and US courts indict two Libyan men, Abdelbaset al-Megrahi and Al Amin Khalifa Fhimah, over the bombing.

However, Libya refuses to extradite them - resulting in an impasse until 1999, when they are handed over after protracted negotiations.

• January 2001: Al-Megrahi jailed for life

Twelve years on from the disaster, al-Megrahi is found guilty of mass murder after a trial at Camp Zeist in the Netherlands, and sentenced to life in prison. Fhimah is cleared of all charges.

The trial, which began in May 2000, was held under Scottish law in the neutral venue and presided over by three Scottish judges.

Following the conviction, al-Megrahi, who had been a Libyan intelligence officer, is sent to a maximum security prison in Glasgow.

• March 2002: Megrahi loses appeal against conviction

Megrahi loses an appeal against his conviction in another special court hearing in the Netherlands.

Libya condemns the decision as a "political verdict".

• August 2003: Libya accepts blame for Lockerbie bombing

Libyan dictator Colonel Muammar Gaddafi accepts blame for the bombing and agrees to compensate the victims' families.

Gaddafi denies that he personally ordered the attack, and Libya says the agreement is dependent on the lifting of UN sanctions - something that follows shortly after.

• March 2004: Blair offers Gaddafi 'hand of friendship'

After talks in a tent outside Tripoli, British Prime Minister Tony Blair offers Colonel Gaddafi the "hand of friendship", prompting a famous photo of the pair shaking hands.Gaddafi says Libya is willing to join Britain in the fight against terrorism, while Blair said there was hope for a "new relationship".

The meeting receives mixed responses from the families of victims.

• May 2007: Britain and Libya sign memorandum of understanding

Talks between Blair and Gaddafi result in a memorandum of understanding being signed, with negotiations beginning on a prisoner transfer agreement.

An oil exploration deal between BP and the Libyan government is signed.

Later in the year, Scottish First Minister Alex Salmond raises concerns that al-Megrahi could be returned to Libya under the transfer agreement, and the UK government agrees to seek a deal which excludes the Lockerbie bomber.

• November 2008: Prisoner transfer agreement signed

The prisoner transfer agreement is signed, with no exclusion for al-Megrahi, who had recently been diagnosed with terminal cancer.

It later emerges that Justice Secretary Jack Straw had decided it was in the UK's "overwhelming interests" not to exclude him from the agreement, which came as Britain and BP were attempting to ratify the £15 billion oil and gas exploration deal in the country.

Libya later says no agreement was made involving al-Megrahi, and a US Foreign Relation Committee finds no evidence of the company attempting to exert influence on al-Megrahi's release.

• August 2009: al-Megrahi returns to Libya

Having rejected a Libyan application under the prisoner transfer agreement, Scotland agrees to release al-Megrahi on compassionate health grounds.

The Scottish government had faced intense pressure over the decision, with US Secretary of State Hillary Clinton urging them not to release him.

A day later, the UK and US both condemn the "hero's welcome" given to the convicted murderer as he arrives in Tripoli amid cheering crowds.

After Gaddafi meets al-Megrahi and praises Prime Minister Gordon Brown for his part in the release, Mr Brown says he is "repulsed" by the welcome and insists the British government had no role in the prisoner's release.

• May 2012: al-Megrahi dies in Libya

The only man convicted over the Lockerbie bombing dies, two-and-a-half years after his release on health grounds.

Following al-Megrahi's death, his family reiterate his innocence, saying that he was a "sacrifice" following the bombing.

• July 2015: Judges rule against al-Megrahi appeal

Scottish judges rule that relatives of some victims of the bombing should not be allowed to pursue an appeal on al-Megrahi's behalf.

The previous year, six members of al-Megrahi's family and 24 British relatives of victims sought a third appeal against his conviction.

• October 2015: Two new suspects identified

Scottish prosecutors announce they are seeking two Libyans identified as suspects in the investigation into the Lockerbie bombing.

ITV News understands them to be Colonel Gaddafi's former spy chief - and brother-in-law - Abdullah al-Senussi and Abu Agila Mas'ud, both of whom are currently being held in a Libyan jail.

Senussi was sentenced to death for crimes against humanity committed during the regime, but the verdict has been under appeal since October 2015.

Senussi is also suspected of involvement in the murder of Pc Yvonne Fletcher outside the Libyan embassy in London in 1984.