Part of the Omagh bomb inquiry is to be investigated by the North's Police Ombudsman, Ms Nuala O'Loan, it was confirmed last night.
Her office is to look into the circumstances surrounding an anonymous telephone call which warned of an attack in the town on the day of the atrocity.
The Ombudsman will be seeking details after it emerged that a former Special Branch officer is to be interviewed by detectives attempting to establish the source of the call.
It was made to police on August 4th, l998, 11 days before the bombing, but the information was never passed to officers.
Relatives of some of the 29 people killed had urged the Ombudsman to carry out her own investigation into the phone call.
Her spokesman confirmed last night that her officers, headed by the executive director, Mr Dave Wood, were on the case.
"The Police Ombudsman's office is now investigating all the circumstances relating to this matter," the spokesman said.
A male caller contacted the CID office in Omagh at 10 a.m. on August 4th, 1998, when he spoke to a detective constable.
He named two men who he claimed would be bringing across the Border four dismantled AK47 rifles and two rocket-launchers belonging to the Continuity IRA which, he said, would be used in an attack on police in Omagh on August 15th.
At the time, the CID officer believed the caller to be genuine, briefed the senior detective on duty and then travelled to Enniskillen, Co Fermanagh, where he informed Special Branch officers. They allegedly told him there was nothing in the information and that the two men named were ordinary criminals.