It is understood a pipe bomb found in a car at Belfast International Airport may have been there for up to a year.
Army bomb experts were called to examine the suspicious vehicle which was discovered in the long-stay car park at about 1430 BST on Saturday.
Police have said they are now investigating the possibility the car had been there since 2009.
The airport parking firm Q Park said "it was confident that car had not been there for a year".
However, the firm said it had not pre-booked and as such was not subject to its automatic number plate recognition software.
In a statement on Monday, a spokesperson for the airport said: "The PSNI are continuing to investigate the exact circumstances around the incident at Belfast International Airport on Saturday 30 October.
"As the incident is the subject of an active police investigation, the airport will not be adding to what the police have already said.
"Speculation as to the events surrounding the incident are unhelpful at this time."
Meanwhile on Monday, Sinn Fein assembly member Mitchel McLaughlin said he "would find it incredible" if the car containing the bomb had been in the car park at the airport for a year.
He said that if there was a viable device "left in a vehicle in such a public place for such a long time, then the implications of that are almost too horrible to imagine".
The alert ended at 0200 BST on Sunday.
The pipe bomb was only discovered because the car was about to be towed away.
Flights were not affected, but some passengers were forced to spend the night in local hotels because they were unable to get home without their cars.
Suspected flammable liquid was found along with the viable device, police said.
It is believed the incident was not linked to bombs left on US-bound cargo planes.
Detectives are investigating a link to dissident republicans as one line of enquiry.
A 40kg bomb was also found on Friday in Lurgan, County Armagh, and Assistant Chief Constable Duncan McCausland said both devices "had the potential to cause injury and damage".
"They were left in places used by the public and with no regard for the public; it is thanks to the vigilance of individuals that no serious harm has been done," he said.