(CNN) - The drone incursion that caused travel chaos for tens of thousands of passengers at London's Gatwick Airport last December could have been an inside job, according to British police.
Based on the behavior of the drone, it is possible the pilot had either first-hand knowledge of the "airport operating environment," or access to that information, Sussex Police said in a statement.
"This has been treated as a credible line of inquiry from the earliest stages of the police investigation and remains one of a number of lines of inquiry," it added.
Gatwick's Chief Operating Officer Chris Woodroofe told the BBC Panorama program that the drone's pilot "seemed to be able to see what was happening on the runway," or was familiar with the airport's operational procedures.
"It was clear that the drone operators had a link into what was going on at the airport," Woodroofe told Panorama in his first interview since the incident.
The perpetrator had "specifically selected" a drone that would fly under the radar of the airport's DJI Aeroscope detection system, which was being trialed at the time, he added.
Woodroofe denied that the airport had overreacted, describing the situation, which caused more than 140,000 passengers to face flight delays and cancellations between December 19 and 21, as "malicious" and "criminal."
"There is absolutely nothing that I would do differently when I look back at the incident, because ultimately, my number one priority has to be to maintain the safety of our passengers, and that's what we did," Woodroofe said.
He also dismissed suggestions that the number of drone sightings was exaggerated.
There were at least 130 separate credible drone sightings recorded by a total of 115 people, including eyewitnesses, police officers, security personnel, air traffic control staff and pilots, police told the BBC.
Woodroofe said many of the drone sightings were by members of his team, "people I have worked with for a decade, people who have worked for 30 years on the airfield, who fully understand the implications of reporting a drone sighting."
Despite a wide-ranging operation and a £50,000 (about $65,500) reward, authorities have still been unable to find the person behind the drone attack. Sussex Police said the investigation was ongoing and was still expected to take "some months to complete."
Since the attack, Gatwick Airport has invested £5 million ($6.5 million) on anti-drone equipment, including two sets of the AUDS (Anti-UAV Defense System) system.
Woodroofe told Panorama that he was confident the airport was now protected: "We would know the drone was arriving on site and we'd know where that drone had come from, where it was going to, and we'd have a much better chance of catching the perpetrator."
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