PSNI and Garda detectives investigating the murder of David Black on the M1 motorway near Lurgan last month have arrested three people north and south of the border.
A 36 year old man was detained in Co Tyrone by PSNI detectives from the Serious Crime Branch.
And in a second planned operation, Gardai from the Special Detective Unit arrested a 31-year-old woman and 44-year-old man in connection with the murder of David Black.
The father of two was shot dead on November 1 as he drove to work at Maghaberry prison in Co Antrim.
A number of other people have been arrested in Lurgan, Tyrone and Co Leitrim but all were released without charge.
The most high profile of the arrests was Lurgan dissident Colin Duffy. He is to sue the PSNI for wrongful arrest and unlawful detention.