Gardaí are questioning a man in relation to a violent attack last month on security men at a house in County Roscommon.
The security firm members had previously forcibly evicted the owners of the farm property at Falsk, near Strokestown.
A large group of people, numbering 15-20, were present during the incident, which detectives believe was orchestrated by individuals linked to dissident republicanism.
Garda sources believe many of those who were there did not know what they were getting involved in and the violence that was due to be carried out by individuals armed with baseball bats.
During the attack up to eight security men were assaulted, some of them requiring hospitalisation.
An alsatian dog, owned by one of the security men, was fatally wounded and three vehicles attached to the security crew were set on fire.
Two men were arrested last month and a third individual, aged 54, was arrested in County Mayo yesterday.
He was arrested under Section 30 of the Offences Against the State Act 1939 as amended.
Gardaí said that investigations into the incident are continuing and more arrests are expected.
It is reported that of the 15-20 that took part in the violent attack, or who were there at the time, six did not wear any balaclavas or did not conceal their faces.
Many of those who took part are believed to have been captured on a CCTV camera getting into a cattle truck and being driven to the home in Falsk in the early hours of December 16.
Gardaí have examined body cameras that the security men were wearing and have identified a number of people of interest.
Sources have told the Irish Examiner that a number of dissident republicans orchestrated the attack and carried out assaults.
The sources said that some other people did not know of the violent intents of the dissidents and may have got caught up in it.