Two drones were used by people with “detailed knowledge” in illegal flybys of Gatwick Airport which caused the major hub to be shut down for 30 hours, according to a police report.
A total of 1,000 flights were disrupted affecting more than 140,000 passengers during the three-day incident which started at 9.07pm on December 19, 2018.
Sussex Police received 129 separate sightings of drone activity, with 109 of these from “credible” witnesses including a pilot, airport workers and airport police.
Two people were arrested from 96 people of interest identified by officers who carried out 1,200 house-to-house inquiries and took 222 witness statements in the police operation which cost £790,000.
The two suspects were later released with no further action to be taken.
A force spokesman said: “The incident was not deemed terror-related and there is no evidence to suggest it was either state-sponsored, campaign or interest-group led. No further arrests have been made.”
He added: “Through corroborated witness statements, it is established that at least two drones were in operation during this period and the offender, or multiple offenders, had detailed knowledge of the airport.
“Witness statements show activity happened in ‘groupings’ across the three days on 12 separate occasions, varying in length from between seven and 45 minutes.
“On six of these occasions, witnesses clearly saw two drones operating simultaneously.”
Assistant Chief Constable Dave Miller, head of operations command, said: “This was a serious and deliberate criminal act designed to endanger airport operations and the safety of the travelling public.
“A drone strike can cause significant damage to an aircraft in flight and it is important to emphasise that public safety was always at the forefront of our response. No aircraft was damaged or passenger injured.
“This was an unprecedented set of circumstances for all agencies involved at a time when the police and the Government were at the early stages of assessing domestic counter drone technology.
“Equipment was quickly installed using both military and private assets to bring it to a conclusion and allow the airport to reopen. Measures now available have strengthened our capability to respond to and investigate a similar incident in the future.”
He added: “With support from national experts, we have carried out an exhaustive criminal investigation but, without new information coming to light, there are no further realistic lines of enquiry at this time.”
The police operation required resources from seven UK police forces as well as national expertise, and Sussex Police is involved in sharing learning from the incident with police and agencies from across the UK and internationally.