Some of the sightings of drones which kept Gatwick Airport on shutdown may have involved the police's own craft, a senior officer has admitted.
Sussex Police Chief Constable Giles York's comment came as he said he was "really sorry" for a couple who were held for 36 hours before being cleared of responsibility for the disruption.
Mr York insisted he is "absolutely certain" a drone was flying near runways at Gatwick during the three-day period from December 19-21 when the airport was repeatedly forced to close.
But he acknowledged there may have been some "confusion" caused by his force launching its own drones in the hunt for the rogue craft.
Speaking to BBC Radio 4's Today programme, Mr York confirmed military technology had been installed at Gatwick following last week's incident, "dramatically" improving security at the airport.
But he acknowledged he could not rule out future disruption of the same kind.
Police have not yet found the drone used to disrupt around 1,000 flights last week and do not know its model, he said.
Two drones found by police near the airport have now been ruled out of involvement.
Mr York said a Sussex officer who suggested last week that police were not sure whether there was a drone flying at Gatwick at all was simply trying to explain the investigative approach taken by the force.
"I am absolutely certain that there was a drone flying throughout the period that the airport was closed," he said.
Police received 115 reports of sightings in the area, including 92 which have been confirmed as coming from "credible people", said Mr York.
But he said: "Of course, we will have launched our own Sussex Police drones at the time with a view to investigate, with a view to engage, with a view to survey the area looking for the drone, so there could be some level of confusion there."
Describing the police investigation as "incredibly thorough", he said: "I don't think we have found the drone responsible for this at this time.
"I think the fact that we have found two drones so far as a result of this does show the extent of the search that has been carried out. I am led to believe that we are able to rule those drones out of this investigation at this time."
The officer also said he felt "really sorry" for Paul Gait and Elaine Kirk, from Crawley, West Sussex, who were detained in the wake of the disruption, but said the grounds for their arrest were "well founded".
The couple have said they felt "violated" by their lengthy questioning, the search of their home and the way in which their identities became public.
Mr York defended the decision to hold Mr Gait for an extended period, despite his employer saying he was at work during the drone flights.
"I'm really sorry for what he has experienced and the feeling of violation around it," said the chief constable.
"I am really sorry for what he went through, but the reason why we held him was so that we could dispel everything in the first instance. What might have been worse as an experience for him would have been to be released under investigation still.
"We are able to exhaust all our lines of inquiry on that first instance and, however hard it is, able to release him from police custody saying he is no longer a suspect in this line of inquiry.
"That's why we took the time - in order to allow him the best opportunity to put his life back on the rails."
Mr York declined to discuss the kind of military technology installed at Gatwick since the drone flights.
"The systems that are in place today are dramatically different to what was in place a week ago," he said.
Asked whether he could rule out a repeat of last week's disruption, Mr York said: "I don't think you can ever rule out anything happening again.
"But what we can say is what is at the heart of this is ensuring it is safe for the aircraft to take off, and that's the different position that Gatwick Airport finds itself in today".