The object, which was the size of a car, was flying at an altitude of 40,000 feet and posed significant risk to civilian flight operations, the National Security Council concluded.
On Wednesday, Longo's wife, who works at a nearby dance studio, got concerned after she couldn't get in touch with her husband, and called the police to run a welfare check.
Flight data provider Flightradar24 said a US P-8A Poseidon aircraft conducted a surveillance mission around Bornholm Island on the morning of September 26.