On the Runs - the key questions over secret IRA lettersWho are the on the runs?
The Northern Ireland Good Friday Agreement of 1998 meant anyone convicted of paramilitary crimes was eligible for early release. However, this did not cover those suspected of such crimes, nor did it cover people who had been charged or convicted but who had escaped from prison.
Negotiations continued after the signing of the agreement between Sinn Féin and the government over how to deal with those known as On the Runs.
Sinn Féin sought a scheme that would allow escaped prisoners and those who were concerned they might be arrested to return to the UK, but a formal legal solution proved difficult to establish in the face of strong unionist opposition.
Against this backdrop, the IRA had still not put its weapons beyond use and Sinn Féin needed grassroots republicans to continue supporting the peace process.How did the government deal with it?
In May 2000, a process to deal with On the Runs was agreed at a meeting between British and Irish officials and Sinn Féin at the Irish embassy in London.
Prime Minister Tony Blair wrote to Sinn Féin president Gerry Adams confirming that if he provided details of the cases, these would be examined by the attorney general in consultation with the police and the director of prosecutions "with a view to giving a response within a month if at all possible".
This was not made public.
Senior legal figures were not happy with the approach. The attorney general wrote to Northern Ireland Secretary Peter Mandelson saying he was "seriously concerned" that the scheme could severely undermine confidence in the criminal justice system.
Mandelson's successor John Reid was also warned by the attorney general in 2002 that it could not become an amnesty and every case would have to be dealt with on the merits of the evidence.Was legislation ever put in place?
In May 2003, proposals about dealing with On the Runs were published as part of a joint declaration by the British and Irish governments. By now the issue was linked with decommissioning of IRA weapons.
Two years later, it was verified by an independent body that the IRA had completely destroyed its arms.
In 2006, an attempt to introduce legislation was shelved in the face of widespread opposition. Sinn Féin's rejection of it, because it would have also covered the Army and police and those guilty of collusion in crimes, made it unworkable.What happened next?
In December 2006, Mr Blair wrote a confidential letter to Mr Adams telling him the government was working on putting in place mechanisms to resolve outstanding On the Run cases, including "expediting the existing administrative procedures".
In February 2007, the Police Service of Northern Ireland (PSNI) began Operation Rapid, the operational name for a review of people regarded as "wanted" in connection with terrorist-related offences before the Good Friday Agreement.
The review examined what basis, if any, the PSNI had to seek the arrest of individuals identified by Sinn Féin to the government and passed to the chief constable.
The then secretary of state, Peter Hain wanted the scheme to be run in secret. The PSNI had prepared a statement for journalists, should the scheme get into the public domain, but the work was never disclosed.Why are we only finding out about this now?
None of this was made public, and details of these assurances only emerged when the deal was brought before an Old Bailey judge.
Mr Justice Sweeney heard from Sinn Féin's Gerry Kelly that 187 people had received letters assuring them they did not face arrest and prosecution for IRA crimes.
John Downey, from Donegal in the Republic of Ireland, was given one of these letters in 2007. Mr Downey denied killing four soldiers in the 1982 IRA Hyde Park bombing.
The judge ruled that he should not be prosecuted because he was given a guarantee he would not face trial.Why was John Downey's letter a "dreadful mistake"?
This was how Prime Minister David Cameron described the letter while addressing the Commons on Wednesday.
John Downey was arrested in May 2013 at Gatwick Airport, en route to Greece, and charged with the murders and bomb attack. He had travelled to the UK on four previous occasions since 2010.
The Old Bailey was told he had received a clear written assurance from the government that he would not be tried.
He cited an official letter he had received in 2007 saying: "There are no warrants in existence, nor are you wanted in Northern Ireland for arrest, questioning or charging by police. The Police Service of Northern Ireland are not aware of any interest in you by any other police force."
He said his alleged offences had been categorised as one of the On the Run cases that would no longer be pursued in the light of progress in the peace process.
The Northern Ireland Office issued the assurance on receipt of information from the PSNI, but while they soon realised he was still wanted by colleagues in Scotland Yard over the Hyde Park bombing, the letter was never withdrawn.
The Crown Prosecution Service had argued that the assurance was given in error - but the judge said it amounted to a "catastrophic failure" that misled the defendant. A trial would therefore be an abuse of executive power.How many of these assurances have been given? Continue reading the main story
sent to Republican suspects
0 letterssent to Loyalist suspects
38 letters sent by current government since 2010
149 sent by previous Labour Government
Last letter sent in 2012
They argue that if people involved in paramilitary crimes during the Troubles can be allowed to walk free, paratroopers involved in Bloody Sunday should not face the courts.
A criminal investigation is currently under way into the killing of 14 unarmed civilians by the Army at a civil rights march in Londonderry in 1972.
It is understood a letter is to be written to the prime minister calling on him to lift the threat of any criminal prosecution against the soldiers.
One MP said: "I'm damned if they should be given an amnesty and former soldiers left hanging there; uncertain over whether they might face prosecution."What will the inquiry involve?
Prime Minister David Cameron said a judge would lead a review that will report by the end of May.
DUP leader Peter Robinson had threatened to resign as Northern Ireland's first minister unless this happened, but after Mr Cameron's announcement, he said he was happy with the inquiry's terms of reference.
It will produce a full public account of the operation and extent of the scheme for On the Runs to determine whether any letters contained errors.
The judge will be able to seek to interview anyone, but will not be able to compel witnesses to attend. Evidence will not be given in public.
It will not alter the decision not to appeal the Downey case.