British police scrambled for answers Sunday after releasing their only suspects in the London Gatwick Airport drone mystery that brought Christmas getaway flights to a standstill.
Nearly 140,000 passengers were affected over three days of disruption Wednesday through Friday as Britain's second-busiest airport shut down because of repeated reports of drone sightings.
A damaged drone found near the airport was being forensically examined, police said, but it was not immediately clear whether it was connected to the sightings.
Police admitted there was a possibility that no drones had, in fact, hovered over the airport as they were relying on eyewitness accounts.
Police arrested a 47-year-old man and a 54-year-old woman from the town of Crawley, near Gatwick, on Friday after a tip-off but released them without charge on Sunday.
"Both people have fully co-operated with our enquiries and I am satisfied that they are no longer suspects in the drone incidents at Gatwick," said Sussex Police detective chief superintendent Jason Tingley.
'Persons of interest'
"We are not back to square one," he said, adding that officers were looking at "persons of interest".
He said that the detectives were investigating 67 reports of drone sightings from the public, police officers and airport staff.
They were also conducting a forensic examination of the damaged drone found near the airport perimeter, close to the location of the last reported sighting, Tingley said.
Asked about speculation that there never was a drone over the airport, he said: "Of course, that's a possibility. We are working with human beings saying they have seen something."
He added: "Our inquiry continues at a pace to locate those responsible for the drone incursions."
The dangers posed by drones include the possibility of a device smashing into a passenger plane or being sucked into an engine where its highly flammable lithium battery could cause a catastrophe.
The airport has offered a £50,000 ($63,000, 56,000 euro) reward for information leading to the arrest and conviction of those responsible for the disruption.
Tingley said the two arrests came after a tip-off from a member of the public, adding that he appreciated the released pair's co-operation in the investigation.
Pictures of the Crawley couple were splashed across Sunday's newspapers, with headlines including "Are these the morons who ruined Christmas?"
While the man was a model helicopter enthusiast, reports inside quoted his astonished boss as saying he could vouch for him having actually been at work throughout the drama.
Under recently introduced laws in Britain, drones cannot be flown near aircraft or within a kilometre (about half a mile) of an airport, or at an altitude of over 400 feet (120 metres).
Violators face up to five years in prison for endangering an aircraft.
Gatwick, around 30 miles (50 kilometres) south of London, is Europe's eighth-busiest airport.
Gatwick's website said its runway was open and it aimed to run a full schedule, but passengers were warned to expect some delays and cancellations.
"Safety is Gatwick's top priority and we are grateful for passengers' continued patience as we work to get them to their final destination in time for Christmas," the airport said.
The main opposition Labour Party has called for an independent inquiry after accusing the government of failing to act on the risks posed by drones.
But a Department for Transport spokesman dismissed claims of missed opportunities to prevent the Gatwick incident as "a combination of nonsense and gross misrepresentation".