LONDON (Reuters) – British police on Sunday released without charge two people arrested in an inquiry into the illegal use of drones at London’s Gatwick Airport that crippled operations for three days last week.

Sussex Police arrested a 47-year-old man and a 54-year-old woman from the local area late on Friday after drones were flown onto the airfield between Wednesday and Friday, forcing about 1,000 flights to be diverted or canceled and affecting 140,000 passengers.

“Both people have fully co-operated with our enquiries, and I am satisfied that they are no longer suspects in the drone incidents at Gatwick,” Detective Chief Superintendent Jason Tingley said on Sunday.

Police said they were actively following lines of investigation to catch those responsible for the most disruptive incursions from unmanned aerial vehicles seen at any major airport.

Drones were spotted at Britain’s second-largest airport on Wednesday evening, forcing it to close its runway in the run up to Christmas. Every time the airport sought to reopen the runway on Thursday, the drones returned.

Authorities finally regained control over the airfield after the army deployed unidentified military technology to guard the area, reassuring the airport that it was safe enough to fly.

The drones caused misery for travelers, many sleeping on the airport floor as they searched for alternative routes to holidays and Christmas family gatherings.

Airlines operating at Gatwick, which is located south of London, include easyJet, British Airways and Norwegian.