Detectives were examining a damaged drone for clues on Sunday night after they had to release two people who were exonerated over the incidents that have repeatedly brought Gatwick airport to a standstill.

Confusion deepened as a senior police officer in the case said it was “always a possibility that there may not have been any genuine drone activity in the first place”. DCS Jason Tingley added that although the damaged drone was a significant line of inquiry, wet weather could have washed away evidence. He also noted that there were no pictures or video of the drone incursions into the airspace around Gatwick . He said there was “no available footage and [officers] are relying on witness accounts”.

Tingley later clarified that police did believe the drone sightings were credible as there had been a large number of witnesses. “We are actively investigating sightings of drone activity at Gatwick airport following 67 reports from the evening of 19 December to 21 December from the public, passengers, police officers and staff at the airport,” he said.

Sussex police said they were not “back to square one” in the investigation after their suspects were cleared and pointed to new persons of interest and house-to-house inquiries near the location of the drone sightings.

The setback to the investigation followed a series of newspaper reports naming those arrested as 47-year-old Paul Gait, a window fitter, and his 54-year-old wife, Elaine Kirk, from Crawley, three miles south of Gatwick.

They were released after 36 hours of questioning. Their friends expressed dismay that the couple had been arrested in the first place.

Their pictures appeared on a number of Sunday newspaper front pages, one of which asked: “Are these the morons who ruined Christmas?” The television presenter Piers Morgan apologised after describing the pair as “clowns” in a tweet and said the situation was a fiasco.

The airport is now offering a £50,000 reward for information leading to the arrest of those responsible.

Sussex police said the damaged device had been found near to the north perimeter of the airport and added that they were fast-tracking tests on it to offer any clues as to who had been flying it.

The series of sightings over the runway had forced Britain’s second-largest airport to shut three times in three days last week, causing hundreds of flight to be cancelled and an estimated 140,000 passengers to be stranded at the airport.

Tingley said the arrests on Friday had followed a tipoff and said police were working through persons of interest.

Sections of the media came under scrutiny for their treatment of the couple, who were surrounded by officers and photographers as they returned to their home on Sunday. Police said they had not put the couple’s names into the public domain.

Police made the arrests just after 10pm on Friday. The man and woman were detained on suspicion of disrupting civil aviation in a way likely to endanger the safety of people or operations.

They were the first arrests made since the drone sightings plunged Gatwick into chaos on Wednesday. It was the airport’s biggest disruption since the Icelandic volcanic ash cloud of 2010.

After the release of the couple, Tingley said in a statement: “Both people have fully cooperated with our inquiries and I am satisfied that they are no longer suspects in the drone incidents at Gatwick.

“It is important to remember that when people are arrested in an effort to make further inquiries it does not mean that they are guilty of an offence and Sussex police would not seek to make their identity public.”

Labour has called for an independent inquiry after accusing the government of missed opportunities to mitigate against the risks posed by drones, claims the government dismissed.

Police and military specialists were deployed to search for those behind the drones, which were sighted again near the airport as the authorities battled to keep the runways open at one of the busiest times of the year.

Airport bosses feared drones could potentially strike passenger planes with catastrophic consequences. The financial consequences of cancelled flights are estimate to run into millions of pounds.

Anti-drone technology used by the army has been brought into Gatwick in an attempt to thwart any further attempts at disruption. British authorities do not believe the incidents were linked to terrorism or any foreign power.