A man (33) who had petrol was poured over him and was set alight at his Armagh home on Tuesday has died in hospital.
The PSNI arrested a man (43) today in connection with the attack. The PSNI said the man was arrested on "suspicion of murder and attempted murder."
Thomas O'Hare and his girlfriend Lisa McClatchey (21) suffered horrific injuries when they were attacked by a gang at the home they shared in Foley Road outside Keady, Co Armagh, on Monday night.
Ms McClatchey remains in a critical condition in the burns unit of the Royal Victoria Hospital in Belfast.
Hours after the fire, four brothers aged between 24 and 34 presented themselves at the accident and emergency unit of Our Lady of Lourdes Hospital across the Border in Drogheda.
All had suffered burns and have since been transferred to a specialist burns unit at St James's Hospital in Dublin where they remain seriously ill.
Police on both sides of the Border have been working to establish whether they were involved in the attack.
The PSNI believe up to six people were involved in the burning. Mystery still surrounds the motive for the attack, but it is believed Mr O'Hare was the main target.