A man who was accused of the murders of four soldiers in the 1982 IRA Hyde Park bombings has been arrested.
John Downey is to be charged with the murder of two other soldiers in Northern Ireland in 1972.
UDR members Alfred Johnston and James Eames were killed in a bomb attack in Enniskillen.
The double murder investigation was re-opened by the PSNI four years ago, shortly after the Hyde Park bomb trial collapsed.
A judgement by Mr Justice Sweeney revealed that the police had uncovered evidence linking Downey to the Enniskillen attack.
But in 1985, prosecutors decided not to seek his extradition from the Republic of Ireland, after evidence alleged to have linked him to the bombing went missing.
A fresh file on the killings was submitted to the Public Prosecution Service in September 2014, and a decision was taken to charge Downey.
Downey was arrested by police in the Republic of Ireland on Monday, 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.
Downey had been due to stand trial in February 2014 over the Hyde Park attack, 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.
Families of the four victims of the Hyde Park bombing are currently suing John Downey.
They are taking a civil action, seeking financial compensation and a finding that he was liable for what happened.
In 1974, Downey was convicted by an Irish court of IRA membership and served time in Portlaoise prison.