Detectives investigating the Castlereagh break-in have travelled to New York to question a former worker at the police base. It is understood the man has already been interrogated by the FBI.
Security sources in the North are insisting the Provisional IRA is linked to the break-in, during which highly sensitive intelligence documents were removed from Special Branch offices. Senior Provisional IRA and Sinn Féin sources are denying the claims and accusing the Police Service of Northern Ireland of "dirty tricks".
Six people, including four republicans and a female civilian employee at the base, were arrested in connection with the incident last weekend.
Five were released without charge. The sixth man, Mr John O'Hagan (29), from north Belfast, was yesterday charged with possession of information likely to be useful to terrorists. The material did not relate to documents stolen from Castlereagh. Mr O'Hagan is denying the charge.
The PSNI mounted new searches on two homes in Ardoyne in north Belfast yesterday. Computer disks and children's clothing were removed from one house. Sinn Féin councillor, Ms Margaret McClenaghan, accused the PSNI of "terrorising" nationalists.
Republican sources insisted the paramilitary organisation played no part in the break-in.
Observers are sceptical the IRA army council would have authorised the Castlereagh break-in because the political fall-out would be much greater than that from any previous incidents. They also doubt the organisation would take such risks to obtain Special Branch files since its campaign is effectively over.
Security sources insisted the arrests of high-profile republicans would not have been carried out during such politically sensitive times - when a second act of decommissioning is expected - unless they had clear evidence implicating the Provisionals.