A five-year-old girl was among crowds of spectators gathered just yards from the car bomb which killed Pc Ronan Kerr before it went off, a police photograph revealed today.
The picture showing the girl waving to runners taking part in the half-marathon right beside the booby-trapped vehicle was released by detectives as they continued to question two men in connection with the murder of the young Catholic officer.
Police believe the high explosive device had already been planted when the image was taken in Omagh, Co Tyrone, on Saturday afternoon.
Two hours later it detonated with devastating consequences when 25-year-old Pc Kerr got into his black Ford Mondeo to go to work.
The officer in charge of the investigation, Detective Superintendent Raymond Murray, said anyone could have been caught up in the blast.
"This device had the potential to kill or maim anyone who happened to be in the area when Ronan got into his car - whether that was him, two men taking part in a fun run or an innocent five-year-old girl watching the race," he said.
"We already know it was murderous. Now we have evidence that it was potentially indiscriminate."
Officers arrested a second man in connection with the murder this morning. The 40-year-old, who was stopped in a van close to Omagh, is also being questioned about a substantial arms and explosives cache uncovered by the murder investigation team in nearby Coalisland on Tuesday night.
A 26-year-old arrested in Dunbartonshire in Scotland yesterday over the weapons haul was re-arrested in police custody in Northern Ireland this morning on suspicion of Pc Kerr's murder.
Meanwhile, police in the Republic carried out a search in an apartment near to Dublin airport as the investigation developed a cross border dimension. No arrests were made.
Officers north of the border returned to the bomb scene this afternoon in a bid to gather information from the community about the 48-hour window prior to the blast.
As they did so the North's Chief Constable, Matt Baggott, warned the killers of Pc Kerr that the hunt to bring them to justice would be relentless.
Again appealing for help from the public, he promised members of his independent scrutiny body - the Northern Ireland Policing Board - a world-class investigation into the murder of the freshly qualified constable.
"It's right that we condemn absolutely those people involved in this brutal murder," he said.
"We will pursue with a world-class investigation and bring them to justice, relentlessly. And I use that word deliberately: it will be relentless."
The weapons haul - found in stolen vehicles in garages on the Mountjoy Road in Coalisland - included Kalashnikov rifles, ammunition, timer power units, detonators, incendiary bombs, components for rocket launchers and other explosive devices, and a quantity of explosives, possibly Semtex.
It is understood one of the cars had an English registration, while police have confirmed that a number of the vehicles had fake plates put on them.
Last September the British government raised the threat of a dissident republican attack in mainland UK to substantial.
However, PSNI Assistant Chief Constable Drew Harris said it was not yet clear where the cars were destined for.
"I'm not sure of the registrations of those cars," he said.
"Four of the vehicles in there were stolen vehicles and some of them had been given different identities but that's all part of our live investigation into where those cars were stolen from, how long they've been there and for what purpose and what was their intention with those."
Mr Harris, who attended the Policing Board meeting in Belfast alongside Mr Baggott, said he was not in a position to establish the origins of the weapons, and if they pre-dated IRA decommissioning.
"At this stage it is too early to say what the age or the vintage or the origin of these weapons and the other material recovered has been, but that's obviously a very live line of inquiry for the investigation which we are pursuing," he said.
While there is little doubt dissident republicans opposed to the peace process were responsible for the murder, no specific renegade group has yet claimed responsibility.
Mr Harris said he was concerned more with individuals than their affiliations.
"No attribution has been claimed in respect of this murder and in fact I am not really focused on groups at moment," he said.
"I am concentrating upon individuals who were involved in this conspiracy to murder but also the wider criminal and terrorist activity that is going on in Tyrone. These groups are fluid, it is pointless that I focus solely on one particular grouping to the exclusion of others."
The developments in the fast-paced investigation came a day after the funeral of the officer heard a plea for an end to violence from Ireland's most senior Catholic churchman Cardinal Sean Brady.
It is believed the intent of the killers was to deter Catholics from joining the police.
But PSNI officers and senior Gaelic Athletic Association (GAA) members stood side by side and helped carry the coffin into the Church of the Immaculate Conception in an unprecedented sign of unity.
Cardinal Brady told mourners: "The people have said no, never again, to the evil and futility of violence. They have said an emphatic no to the murder and mayhem of the past. Let there be no doubt that the killing of Ronan Kerr was totally unjustified."
At today's board meeting, Mr Baggott said the pictures from the funeral had provided a vision of what a shared future looked like.
"I hope it is of some comfort to Ronan's family and everybody who knew him that we saw yesterday what I would describe as a new reality of policing; policing that is increasingly involved with communities, intimately involved," he said.
"The relationships that we saw yesterday haven't just taken place in a few days they have been built by people talking and listening and being prepared to take risks."
He added: "Yesterday as I saw red (GAA) jerseys alongside PSNI officers with young people, politicians and most importantly just the people who live there coming out in huge numbers to support Ronan's family is the new reality of policing.
"And it's a policing that is personal and it is a policing that is involved and I do think yesterday we saw something of the shared future and that is something that myself and my colleagues, everybody that works for this great organisation that is ten years old, will redouble our efforts to make sure that that is never lost."
A minute's silence was held before the meeting at board headquarters in Belfast got under way.