UK police are investigating "a number of lines of inquiry" after a drone intrusion closed Gatwick, the UK's second busiest airport, for more than a day, according to a BBC report.
The police are currently focusing on examining "likely locations in and around the airport" from which the drones that flew over the airfield, grounding many flights, could have been operated.
Some 837 flights have been cancelled over the incident, and incoming flights have been redirected to airports both inside the UK and across the EU.
The police have ruled out terrorism as a motive for the intrusion and say that "involvement of a foreign power" is unlikely, too. One of the possible motives the police are examining is environmental activism.
"This is a really significant criminal offense," he told reporters.
Barry also disclosed that the police assume that there was more than one drone operating around the airport.
"In terms of how many perpetrators, there's a number of lines of inquiry. There's an ongoing investigation; we're pursuing that, trying to find out who has been responsible for this really malicious criminal behavior," he said.
He also said the police have identified "persons of interest" as part of the investigation, but no arrests have reportedly been made so far.
According to Barry, the authorities mulled various means to tackle the threat, from "technical, sophisticated" solutions created to "detect and mitigate drone incursions," to some "less sophisticated solutions," such as blowing the drones out of the sky with shotguns.
"Coordinating that, deploying that, getting it set up at Gatwick has taken some time, but we've learnt from that," Barry said.
According to UK laws, it is illegal to fly a drone above 120 meters or within 1 kilometer of an airport. Violation of these restrictions is viewed as endangering the safety of an aircraft and is punishable by up to five years in prison.