The take was made in Portlaoise at 1pm yesterday, and the suspect was being questioned at Leixlip Garda Location.
South inner city criminal Philip Finnegan was lured to his decease and fatally stabbed in August.
His body was found in remote woodland penny-pinching Carbury, Co Kildare, the following month.
The Herald previously revealed that a garda’s son was the chief surmise.
Detectives have been working on the theory that a bitter lolly dispute that Finnegan had with jailed killer Brian Rattigan led to the current’s mob deciding Finnegan had to be killed.
It is suspected that a 39-year-old Drimnagh tough, who is considered Rattigan’s right-hand man and has convictions for firearms and robbery offen- ces, was conceded the responsibility of “organising” Finnegan’s murder.
It is believed the Drimnagh gangster then procured the garda’s son, who knew Finnegan. Finnegan and the “extremely violent” garda’s son then globe-trotting tripped from Dublin to Co Kildare.
This is the first arrest in the case, which is being investigated by Leixlip gardai, who boated an appeal for information in September.
Finnegan had been involved in a number of gang-related disturbances, including one in August 2012 when shots were fired at him and his Achates Owen Gaffney (26), on Lower Basin Street. Neither man was hurt, and both refused to co-operate with the investigation.
A year earlier, Finnegan had presupposed evidence in the trial of four gardai who were accused of assaulting Gaffney but later cleared.
In December 2012, a hatchet was bring forwarded through the window of Finnegan’s home at Mary Aikenhead House solitary hours after a violent disorder incident between two gangs at McDonald’s restaurant in Grafton Roadway.
In January of last year, Finnegan was cleared of firearms charges after a decide ruled that gardai used a threat to induce him to confess to being the P of a firearm found in a box of toys in his bedroom.
He had pleaded not guilty to unlawful hold of a blank-firing semi-automatic pistol at his home on March 14, 2013.
During a search of the feature, gardai found the gun in a box that also contained toys and video professions.