A man has been arrested in Co Donegal in connection with the 9 February murder of Andrew Allen.
The man, aged in his 30s, is being detained under Section 30 of the Offences Against the State Act, 1939, at Buncrana Garda Station.
Mr Allen was shot dead at his home at Links View Park in Buncrana.
He was shot through a window after a group of men tried to break down the front door.
The attack has been blamed on the Republican Action Against Drugs group.