Convicted garda killer Aaron Brady has been arrested on suspicion of witness intimidation in connection with his murder trial.
The 29-year-old was taken from prison by gardaí this morning and is being questioned at Portlaoise Garda Station.
He can be detained for up to 24 hours.
He is the seventh person to be arrested as part of a garda investigation set up after a number of witnesses did not give evidence during the trial.
The presiding judge called it the most outrageous contempt of court he had seen.
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Brady was taken from his cell at Portlaoise Prison early this morning by detectives from the National Bureau of Criminal Investigation and brought to the local garda station in Portlaoise.
The 29-year-old from Crossmaglen in Co Armagh has been convicted of the murder of Detective Garda Donohoe and is serving life in prison with a minimum of 40 years.
Earlier this year a court heard that Brady gave the detective and father-of-two "no chance" when he shot him in the head during an armed robbery at the Lordship Credit Union in Co Louth seven years ago.
He is being questioned as part of an investigation into witness intimidation, perverting the course of justice and the unlawful use of mobile phones in prison related to the his recent trial for the murder.
Following his conviction It emerged that a video of one witness giving a statement about him to gardaí was circulated on social media with text calling him a "rat" and accusing him of "touting" on his friends.
The witness did not come forward to give evidence.
He was one of five witnesses who did not testify in the trial at the Central Criminal Court during which there were repeated claims that witnesses were being interfered with and intimidated.
Mr Justice Michael White called it "the most outrageous" contempt of court he had seen in his career.
Brady is the second person arrested in the past 24 hours and the seventh so far in connection with the witness intimidation investigation.