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 over the murder of the young Catholic officer.
Police believe the high explosive device had already been planted when the image was taken in Omagh, County 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, Det Supt 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 on Wednesday 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.
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.
Police were yesterday continuing their inquiries among the community in Omagh.