A senior Liverpool police officer is to oversee an investigation into the 1998 Omagh bombing which killed 29 people, including a woman expecting twins.
Mr Mike Tonge, the Deputy Chief Constable of the Merseyside force, is to "quality-assure" an investigation headed by the PSNI's Mr Brian McArthur.
A parallel investigation headed by another Liverpool officer, Mr Philip Jones, is also under way.
Mr Tonge will retain his duties with the Merseyside force and will work in Northern Ireland a few days per month.
The arrangement was concluded on Thursday night following a meeting with the chairman and vice-chairman of the Policing Board which oversees policing in the North. Mr Tonge will now answer directly to the 19-member board, which includes both independent and party-political appointees.
It is thought the move to have two senior Liverpool detectives working on the Omagh case was resisted by other Merseyside officers, who were concerned about a drain on their force's resources. But Policing Board sources are understood to have been strongly in favour of the duo being involved in the North as they had worked together in England.
The idea of two investigations running in tandem and under scrutiny from an outside officer arose in response to the critical review of the RUC/PSNI investigation into the "Real IRA" atrocity by the police ombudsman, Mrs Nuala O'Loan.
The former chief constable, Sir Ronnie Flanagan, insisted Mr McArthur remained at the head of the inquiry, whereas Omagh victims' families and nationalist members of the board wanted a new officer in charge.
Sir Ronnie has now joined Her Majesty's Inspectors of Constabulary, the police watchdog in England and Wales, which named Mr Tonge to oversee the Omagh inquiry. It is understood Prof Desmond Rea and Mr Denis Bradley of the Policing Board had pressed for Mr Tonge to be named for the position.