Police have seized mobile phones and documentation in searches carried out as part of the investigation into Detective Garda Adrian Donohoe's murder outside a credit union in January.
Armed members of the PSNI raided four houses in south Armagh and took away the material for forensic examination.
Officers disclosed that the searches had been intelligence-led and were focused on suspected criminals or associates of members of the gang believed to have been responsible for the murder of the father of two in Lordship, near Dundalk, on January 25.
The raids were part of ongoing inquiries by the PSNI and gardai into gangs operating in the border region around counties Armagh, Down, Louth and Monaghan.
Two men have already been questioned by gardai in relation to suspected links with the gang.
A reward of €50,000 for information has been offered by the Irish League of Credit Unions, while Crimestoppers have put up a further five-figure sum for help that could progress the police investigation.
Gardai are satisfied that five members of the gang were present at Lordship when Det Gda Donohoe was shot dead with a long-barrelled shotgun as he stepped out of a garda escort car to establish why the exit of the credit union car park had been blocked.
The identities of all of the key suspects have been established.