Police have blamed “poor communication” for confusion over the Gatwick Airport chaos after saying it was possible there was never a drone at the airport.
It comes after ministers were briefed on the latest situation at the airport in an hour-long conference call on Monday, chaired by Transport Secretary Chris Grayling.
On Sunday, Sussex Police said it was a "possibility" that there might never have been a drone despite the massive disruption in the run-up to Christmas.
Detective Chief Superintendent Jason Tingley told the BBC: "Of course, that's a possibility. We are working with human beings saying they have seen something.
Gatwick chaos - In pictures
"Until we've got more clarity around what they've said, the detail - the time, place, direction of travel, all those types of things - and that's a big task."
However, following the call, a government source said police accepted that there had been "poor communications".
In a new statement on Monday, Sussex Police said there had "unequivocally" been numerous sightings of unmanned aircraft over three days in the run up to Christmas.
Sussex Police Deputy Chief Constable Jo Shiner said: “We can unequivocally state that there have been numerous illegal drone sightings at the airport over three days from 19 to 21 December.
“There were numerous reports clustered around 37 occasions where a drone or drones were seen and I am keen for those responsible to be brought to justice.”
The force listed sightings of the drone as it appealed for information relating to the drone.
DCC Shiner added: “The impact of this criminal and reckless behaviour has been enormous and we are determined to locate those responsible to bring them to justice. We are investigating this under the Aviation and Maritime Security Act which carries a maximum sentence of life imprisonment.
“We urge the public to contact us if they feel they have information that will help us in our investigation. Contacting Crimestoppers they can do this anonymously. We ask the public to continue to support us by reporting any suspicious activity.”
There were more than 200 drone sightings, and police had taken 67 statements, including from police officers and airport workers.
Some 140,000 people were affected as around 1,000 flights were delayed or cancelled as a result of the chaos, which began on Wednesday and lasted for three days.
It comes as detectives examine a damaged drone found nearby while Gatwick Airport has offered a £50,000 reward, through Crimestoppers, and another £10,000 has been put up by the charity's chairman Lord Ashcroft to catch those responsible.
Mr Tingley also said on Sunday there were some "persons of interest" but would not reveal if police were close to making any further arrests.
He added there is no video footage available and investigators were trying to confirm sightings from members of the public, police officers and ground staff, as well as forensically examining the damaged drone found near the runway's perimeter, in Horley, by a member of the public.
