Detectives are examining a damaged drone found close to the last reported sighting at Gatwick Airport after two people held over the disruption were released without charge.
The 47-year-old man and a 54-year-old woman were arrested on Friday after a tip-off from a member of the public, while their house in nearby Crawley was searched.
Sussex Police insisted the force was “not back to square one” after ruling out the pair – who made no comment as they darted inside their home on Sunday morning – as suspects.
Gatwick Airport has offered a £50,000 (€55,500) reward, through Crimestoppers, and another £10,000 (€11,000) has been put up by the charity’s chairman Michael Ashcroft to catch the culprits responsible for the chaos, which affected around 140,000 passengers.
Detective Chief Superintendent Jason Tingley said he hoped the money would persuade someone to come forward with the vital clue.
“We are actively investigating sightings of drone activity at Gatwick Airport following 67 reports from the evening of December 19 to December 21 from the public, passengers, police officers and staff at the airport,” he said.
“We are interviewing those who have reported these sightings, are carrying out extensive house-to-house enquiries and carrying out a forensic examination of a damaged drone found near the perimeter of the airport near Horley, which is close to the last reported sighting.”
He said there were some “persons of interest”, but would not reveal if police were close to making any further arrests.
Around 1,000 flights were cancelled or diverted after drones were spotted inside the perimeter of the UK’s second biggest airport on Wednesday.
Mr Tingley said there is no video footage available and investigators are relying on 67 drone sightings by witnesses.
Asked about speculation there was never a drone, he said: “Of course, that’s a possibility. We are working with human beings saying they have seen something.”
Mr Tingley said police were running a three-pronged investigation including working through information relating to “persons of interest”, investigating sightings and forensically examining the damaged drone, which was spotted by a member of the public.
But he explained the examination could be hampered by the wet weather on Friday and Saturday, which could have washed away evidence.
And he could not rule out the risk the culprits would strike again at Gatwick or another airport.
“Someone, somewhere knows either the perpetrator or perpetrators responsible for this, or has information relating to these incidents,” he said.
“But secondly, our tactical response, should there be any more drone sightings, is still in place.”