Police in the UK says they have no more "realistic lines of enquiry" in their investigation into the Gatwick Airport drone attack.
Nobody has been charged in connection with the investigation.
Gatwick Airport had to close for 30 hours across several days last December in the run-up to the Christmas.
Hundreds of flights were disrupted, impacting around 140,000 passengers.
In an update on their investigation, Sussex Police said they've concluded that at least two drones were involved.
They say witness statements have led to the belief that whoever was behind the attack had detailed knowledge of the airport.
Detectives identified, researched and ruled out 96 people ‘of interest’ - but now say they have no path forward in the investigation.
Assistant Chief Constable Dave Miller said: “This was a serious and deliberate criminal act designed to endanger airport operations and the safety of the travelling public.
“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.”
Police say their Gatwick policing operation and subsequent investigation cost £790,000 (€888,000), mostly from the "operational police response".