Detectives investigating the Northern Bank robbery are trying to establish if the white box-type Ford van used by the gang was stolen in Wales.
The PSNI said last night that this was "a strong line of inquiry" and that it remained a "priority to establish the origins of the vehicle".
The van, which bore what the police call "ringer" or duplicated number plates, was driven north across the Border and was spotted shortly before 5 p.m. just south of Newry, Co Down, on the day of the robbery.
The white Ford van with an unusual box-type design and a tailgate lift may have been stolen in Gwent some two weeks before the £26.5 million theft on December 20th.
The van, bearing the registration RCZ 6632, has not been seen since it left Wellington Street near Belfast City Hall with a second haul of banknotes from the Northern Bank's cash centre. It was picked up by CCTV heading north along College Square.
Police have issued appeals for information concerning its whereabouts. The number plates are connected with another white van "which is owned by a company in Belfast and which regularly makes deliveries around the Newry area", according to a senior investigating source.
The robbery has prompted the Independent Monitoring Commission to compile a report on paramilitary activity which is expected to be published shortly - well ahead of its next scheduled publication date in April. The commission is to meet the Taoiseach, Mr Ahern, on Monday before deciding on the question of sanctions later in the week. It will also then decide when to release its latest findings in relation to the theft.
Sources have told The Irish Times that the commission was not asked by the two governments to compile a specific report on the Northern Bank theft. It is understood that its report will endorse the assessment by the Chief Constable, Mr Hugh Orde, that the IRA was responsible.