Two men have been arrested by police investigating the murder of a prison officer from Cookstown.
David Black, a father-of-two, was shot dead on the M1 in County Armagh on 1 November 2012 as he drove to work at Maghasberry Prison in County Antrim.
Searches were carried out in the Republic of Ireland in an operation against dissident republicans.
The operation centred on the Leitrim and Cavan areas and two men, 51 and 34, have been arrested.
Mr Black, 52, was the first prison officer to be murdered in Northern Ireland in almost 20 years.
Mr Black was attacked between Portadown and Lurgan on the M1, about a mile from Lurgan exit.
A dark blue Toyota Camry with a Republic of Ireland registration, 94 D 50997, pulled alongside and a number of shots were fired, killing Mr Black.
The Toyota Camry was found burnt out in the Inglewood district of Lurgan a short time later.