A man who was accused of carrying out a 1982 bombing that killed four soldiers has been arrested over two other murders.
Police in Northern Ireland said John Downey has been arrested on suspicion of murdering two Ulster Defence Regiment (UDR) soldiers in a bomb attack in Enniskillen in 1972.
He is also accused of aiding and abetting an explosion.
The 66-year-old is expected to appear at Dublin High Court on Tuesday.
In 2013, Downey, from County Donegal, was charged with murdering four Royal Household Cavalrymen with a bomb in Londons Hyde Park, but his trial dramatically collapsed.
A spokesman for the Public Prosecution Service for Northern Ireland said: Following careful consideration of all available evidence, a decision has been taken to prosecute one person for the offence of murder and for aiding and abetting the causing of an explosion.
Extradition proceedings were initiated in the High Court in Dublin on Monday November 5, to seek the extradition of one man from the Republic of Ireland for trial in Northern Ireland.
One man was subsequently arrested in County Donegal this evening and is due to appear in court in Dublin tomorrow.
Downey has always denied involvement in the Hyde Park attack.
He was freed after it was revealed he received a written assurance from former prime minister Tony Blairs government that he was not actively wanted by the authorities.
Trial judge Mr Justice Sweeney ruled that Mr Downeys arrest at Gatwick airport, as he transited the UK on the way to a holiday, represented an abuse of process and he put a stay on any future prosecution in relation to the Hyde Park case.