LONDON — The tally so far: Britain’s second-busiest airport stalled for 36 hours. About 1,000 flights diverted or canceled. Around 140,000 passengers inconvenienced at the height of holiday travels.

That was last week, when British officials said that drones had been spotted flying near Gatwick Airport, south of London, and shut it down.

The score since then? One broken drone recovered, and a British couple detained and then released over the weekend without being charged.

If the investigators seem flummoxed, they are.

The fact that Gatwick is one of the most heavily surveilled strips of land in England, combined with an absence of video of any drone, left the lead investigator, Detective Chief Superintendent Jason Tingley, questioning whether drones were in fact involved at all.