Published Friday, 07 September 2012
Gardai are questioning the man over the killing of Alan Ryan. (© Getty)
The dissident republican was gunned down close to his home in north Dublin on Monday afternoon.
Armed Gardaí have been on patrol since the killing and have stepped up security ahead of his funeral at The Church of the Holy Trinity in Donaghmede on Saturday morning.
Gardaí in Coolock arrested a man in his 40s on Wednesday night.
They haven't disclosed where he is being questioned.
A spokesman said he is being detained at a north city Garda Station under Section 30 Offences Against the State 1939 where he can be held for up to three days.
Ryan, 32, was one of the leaders of the RIRA Dublin branch and, with other members, had been trying to extort money from drugs gangs.
Detectives are trying to establish if a number of gangs organised and paid for his murder in the Grange Lodge estate in Clongriffin.
They fear there may be revenge for his killing.
A convicted criminal, Ryan was notorious for racketeering - extorting cash from drug dealers and businessmen across the city and demanding protection money from firms.
He was jailed for taking part in a RIRA weapons training camp in Meath in 2001 and served time for possession of a firearm in a separate incident.
At the time of his murder Ryan was due to go on trial for an alleged extortion racket and for threatening a Dublin publican and forcing him cease trading within 24 hours.