(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.

Read More