The men behind the Omagh bomb could have been arrested before the atrocity, the man who investigated the murders said last night.
Norman Baxter said had intelligence services shared information with the police, the lives of the 29 killed could have been saved.
Mr Baxter gave evidence to the Northern Ireland Affairs Committee of MPs and said there had been a string of earlier threats involving the same republican gang.
"The investigators didn't have access to the intelligence, not to prevent those incidents, but to ensure that the investigators after those incidents would have had an opportunity to have the suspects arrested prior to the Omagh bomb," he said.
The former detective superintendent said the Real IRA team came from Northern Ireland and the Republic of Ireland.
"These bombers then had free reign from the middle of 1997 and the authorities, whoever they were, allowed that to continue," he added.
He said there were earlier bombs in Markethill, Co Armagh, Moira, Co Antrim, Portadown, Co Armagh, and Lisburn and Banbridge, Co Down.
"At each one of those terrorist incidents there was a point of intervention which could have disrupted this terror gang," he added.
"There could have been opportunities to arrest this gang after Lisburn, after bombs in May (1998), July and even after Banbridge.
He added: "The investigators didn't have access to the intelligence."
He said there was intelligence relating to 16 terrorist incidents which he did not believe was shared with investigators after those incidents.
Mr Baxter said any telephone numbers of suspects should have been provided to his inquiry.
"Omagh can't be seen as an individual incident, Omagh was the last in a series of incidents dating into the middle of the 1990s, the middle of 1997, and so there's a long lead-in to the Omagh explosion," he warned.
He added: "The information sits behind the intelligence which may have been of value in the early days of the inquiry."
Intelligence Services Commissioner Sir Peter Gibson has said information on the bombers was shared with police following his review ordered by the Prime Minister, but could not have stopped the 1998 attack.
In his report, Sir Peter said details from telephone intercepts were passed on "promptly and fully" and in accordance with proper procedures.
A BBC Panorama programme had claimed that intelligence officers based at GCHQ had monitored the bombers' phone calls, but had failed or refused to pass information to Royal Ulster Constabulary (RUC) detectives hunting the killers in the days following the attack.
But Mr Baxter told the committee Sir Peter's terms of reference were "far away" from the inquiry which Gordon Brown announced following claims that vital intelligence was deliberately held back.
"The expectations of the families who are still seeking closure were raised to a point that Sir Peter couldn't meet," he added.