A man who was accused of the murders of four soldiers in the 1982 IRA Hyde Park bombings has been arrested.
John Downey has been arrested on suspicion of the murder of two other soldiers in Northern Ireland in 1972.
His trial for the Hyde Park murders collapsed because of a secret letter from the government which gave him a guarantee he would not face trial.
He was arrested by police in the Republic of Ireland using a European Arrest Warrant.
The PSNI confirmed detectives from An Garda Siochana (in a joint operation with the PSNI) had arrested a 66-year-old man in Donegal on suspicion of the murder of two UDR soldiers in 1972 and on suspicion of aiding and abetting an explosion.
He is due to appear at Dublin High Court on Tuesday afternoon.
The 66-year-old had been due to stand trial in February 2014, but the trial collapsed because he was wrongly told he was not wanted by the police.
The County Donegal man had been sent a so-called “on the runs” letter which said he was not wanted for arrest, questioning or charge by the police.
Even though the letter was factually wrong, a judge at the Old Bailey in London said it was a legally binding assurance that he would not be prosecuted.
Downey was one of about 200 republicans to receive the letters as the result of a deal between Tony Blair’s government and Sinn Fein.
Former First Minister and DUP leader Peter Robinson described the letters as “get out of jail free cards”.
But the government and police insisted they did not amount to a promise of immunity from prosecution and said recipients could face charges if new evidence emerged.