Gardaí are questioning a man as part of their investigation into the murder of Vincent Ryan (pictured).
The man in his 30s was arrested in Dublin yesterday afternoon.
Twenty-five-year-old Vincent Ryan was shot dead on February 29 as he sat in a car on the McKee Road in Finglas on Dublin's northside.
He was the brother of Real IRA boss Alan Ryan who was killed in 2012.
Yesterday, gardaí arrested a man in his 30s under section 30 of the Offences Against the State Act.
He is being held at Finglas Garda Station where he can be kept for up to three days.