Two men are still being questioned by police over the murder of Northern Ireland police officer Ronan Kerr and an arms find in County Tyrone.
Constable Kerr, 25, was killed when a car bomb exploded in Omagh on Saturday.
A 40-year-old was arrested when a van was stopped near the Beragh turn-off on the Ballygawley line in County Tyrone on Thursday.
A 26-year-old man arrested in Scotland on Wednesday under the Terrorism Act was re-arrested over Mr Kerr's murder.
A house in Dublin has also been searched in connection with the murder.
The search was carried out by members of the Garda (Irish police) Special Detective Unit at the request of the Police Service of Northern Ireland.
The search was at a property on the north side of Dublin, close to the airport.
Weapons and explosives were found in the Coalisland area of County Tyrone on Tuesday evening by police investigating the police officer's murder.
The arms found were:
• Four Kalashnikov rifles
• Six loaded ammunition magazines
• Timer power units
• Incendiary bombs
• Components for rocket launchers and other explosive devices
• Quantity of explosives, possibly Semtex
BBC NI home affairs correspondent Vincent Kearney said it had been a significant length of time since the police had uncovered an arms haul of this quantity and variety.
He added that if it turned out that the explosives found were Semtex, it would raise questions about whether dissidents had access to a new supply line or whether the explosives formerly belonged to the Provisional IRA.