UK police have admitted the mystery drones which disrupted operations at Britain's Gatwick Airport might not have ever existed.
About 1000 flights were diverted or cancelled, affecting 140,000 passengers, after one or more drones were believed to have been flown on to the airfield between Wednesday and Friday.
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But Detective Chief Superintendent Jason Tingley told the BBC that there was "no available footage" of the drones and it was "always a possibility" that sightings were wrong.
"[There is] always a possibility that there may not have been any genuine drone activity in the first place," he said.
"Of course, that's a possibility. We are working with human beings saying they have seen something."
The 47-year-old man and 54-year-old woman arrested on suspicion of being behind the drone activity have been released without charge.
"Both people have fully co-operated with our inquiries, and I am satisfied that they are no longer suspects in the drone incidents at Gatwick," Detective Chief Superintendent Tingley said.
He said he was confident the arrests were justified.
Police are now investigating a damaged drone device discovered near the airport. But the Daily Mail reports that a source told them that the drone could be a "red herring" and it could have been there for a while.
The airport is now offering a €50,000 (NZD$94,000) reward for information leading to the real culprits.