A Kinahan cartel linked gangster was one of four criminals being quizzed last night over a campaign of intimidation during the Adrian Donohoe murder trial.
Notorious north inner city criminal Glen Holland (36), who is aligned to the international crime gang, was arrested in Mountjoy Prison yesterday.
He and three others were all being questioned at different Dublin garda stations.
Also arrested in the same jail was Dean Byrne (25), a north Dublin criminal with over 120 convictions who is currently serving a lengthy sentence for aggravated burglary.
The Herald previously revealed details of searches in their cells in July and August when detectives from the National Bureau of Criminal Investigation (NBCI) were backed up by the jail's Operational Support Group (OSG).
An illegal mobile phone, a charger and notebooks were seized in a cell of Holland's in late August.
Glen Holland is serving a six- and-a-half year sentence after pleading guilty to possessing two loaded handguns as well as almost €70,000 worth of cocaine in September 2010.
He was previously arrested by detectives investigating the murder of Eamon 'The Don' Dunne in April of that year and spent over six years on the run in the UK and Spain before being arrested in Spain in August 2017, on foot of a European Arrest Warrant.
"Key evidence was seized and this may prove to be very useful in the ongoing witness intimidation investigation," a senior source said at the time of the search of Holland's cell.
Also arrested yesterday was a close associate of Coolock criminal Jamie Tighe (24), who was shot dead as part of a northside feud in October 2017.
Tighe's associate was previously jailed for four years for firearms offences. He was already serving a jail term for violent disorder and was on bail for this crime when he was arrested.
Aaron Brady (29) will be sentenced to the mandatory term of 40 years in jail for capital murder at the Central Criminal Court next week.
He was convicted after a lengthy trial, which was blighted with witness intimidation.
Even before it ended, the NBCI had begun a detailed probe into the intimidation.
Five witnesses did not give evidence in the trial, during which there were repeated claims witnesses were suffering intimidation.
Following the conviction, it emerged that a video of one witness giving a statement about Aaron Brady to gardaí was circulated on social media with text calling him a "rat".
In mid-July, Detectives searched the Mountjoy cell of Dean Byrne (25) and while no phone was found, a piece of paper with several phone numbers scrawled on it was seized.
Gardaí are investigating if the intimidation of certain witnesses was "outsourced".
"Gardaí attached to the Serious Crime Review Team in the Garda National Bureau of Criminal Investigation (GNBCI) arrested four persons in relation to this investigation." a garda spokesperson said yesterday.
"All four are currently detained in Mountjoy, Ballymun, Bridewell and Raheny Garda Stations respectively, for the investigation of the offences concerned," she added.