A member of the so-called Friday Night Gang of border associates of Garda killer Aaron Brady has been arrested in connection with the 2013 murder of Detective Adrian Donohoe.
The man, originally from Newry and in his 30s, was arrested in the Dundalk area shortly before 8.30am yesterday and is being questioned in the town's Garda station.
He was one of the five suspects An Garda Siochana vowed to actively pursue in relation to the case.
The suspect had been living in the Republic and is a known associate of Brady's.
He also has known links to dissident republicans operating along the border.
Garda Detective Donohoe was shot dead during a robbery at Lordship Credit Union in Co Louth on January 25, 2013.
Last October Brady, of New Road, Crossmaglen, Co Armagh, was sentenced to life in prison for the murder of the popular police officer following the largest investigation of its kind involving police forces in three jurisdictions.
Convicted of capital murder, he will serve at least 40 years before being eligible for parole.
Brady was also sentenced to 14 years for armed robbery.
The killer fled to the United States around two months after the shooting and began working for a firm in Boston before moving to New York in 2014.
He married a local woman and had a child.
In the months before his arrest, and unknown to him, he was under surveillance by officers of the New York Police Department's Intelligence Bureau.
In the early hours of May 18, 2017, US Marshals and officers from US Immigration and Customs Enforcement swooped on Brady in the Yonkers area of New York.
He was later extradited to stand trial.
Detective Donohoe was married with two young children.
He was one of two officers on late-night duty escorting a cash collection at the rural credit union when the robbery took place.
The police escorts had been put in place following a series of weekend robberies by Brady and his associates, who were also heavily involved in other forms of cross-border criminality, including smuggling, robbery and theft of high performance car parts.
The gang had been responsible for ATM thefts on both sides of the frontier.
The raids, often involving stolen diggers, took place on a Friday evening when they knew the cash machines had been filled for the busy weekend, earning them the name the Friday Night Gang.
Following Brady's conviction last August detectives said the investigation was far from over and they intended to pursue five more men implicated in the killing. Deputy Commissioner John Twomey warned all those involved in the credit union robbery that investigators "will be knocking on your door and make sure that you pay for the horrendous act".
The suspect is the first of the gang of five to be targeted in what is expected to be a spate of arrests.