Four men remain in Garda custody this morning in connection with the abduction and torture of Kevin Lunney.
Three of the men were detained in Dublin yesterday, while another was arrested in Cavan.
The vicious attack on Kevin Lunney in September this year left the Quinn Insurance Holdings director with life-changing injuries.
The 50-year-old was abducted outside his home in Derrylin, Co. Fermanagh, and found hours later on a roadside in Cavan, bleeding and freezing.
He had a broken leg and had been slashed with a knife, doused with bleach and branded by the attackers.
Yesterday four men - two aged 38, one aged 25 and another aged 66 - were arrested in Dublin and Cavan in connection with the investigation.
The chief suspect, Cyril McGuinness, died during a police raid in the UK earlier this month.
Sinn Féin's justice spokesperson, Martin Kenny, says there's a sense of relief that gardaí seem to be finally making progress in the investigation.
Mr Kenny said: "This has been a long drawn-out saga going on for many years and many people in the public and the community in the border region have been very distressed by what has happened.
"Having said that, I think there is a certain confidence coming back into it that finally the gardaí seem to be getting a handle on it."
A total of seven people, including a mother and son, have so far been questioned in connection with the attack.