Maksim Kuzminov pulled off a daring escape last summer when he defected to Ukraine and handed his military helicopter over to Ukrainian commandos in exchange for half a million dollars.

Ukraine trumpeted the defection as a major coup. But in Vladimir V. Putin’s Russia, he was guilty of the most grievous sin anyone can commit: Treason. Ukrainian intelligence officials warned Mr. Kuzminov that his life was in danger and urged him not to leave the country.

But he ignored them, and was believed to have moved with his money to a small resort town of pastel houses on Spain’s Mediterranean coast.

Now Mr. Kuzminov, 28 at the time of his defection, appears to have met the harsh fate Ukrainian officials warned of. Two Spanish police officials with knowledge of the case said the body of a man found riddled with bullets last week in the coastal town of Villajoyosa belonged to Mr. Kuzminov.

Andriy Cherniak, a representative of Ukraine’s military intelligence, also said he could “confirm the fact of his death,” referring to Mr. Kuzminov, but he declined to elaborate on the circumstances.

Authorities released no information about possible assailants or a motive, and they have not publicly confirmed the identity. The case has been complicated by puzzling statements issued by the Civil Guard, a branch of Spain’s national police forces, which at one point said the papers found on the body identified him as a 33-year-old Ukrainian man. But they added that the documents may be fake.