Spanish intelligence officials believe killers sent by Moscow are responsible for the shooting death of a prominent Russian soldier who deserted from the army last year in a chopper he stole from Russian forces near Ukraine.

According to a report in Spain’s El Pais newspaper, the assassination of Maxim Kuzminov February 13 near a coastal resort favored by Russian nationals, was “almost certainly” carried out by Russian operatives who have since fled the country.

“The Spanish intelligence services have no doubt that the long arm of the Kremlin was behind this unprecedented crime in Spain,” the paper said.

Kuzminov’s body was found riddled with six bullets in Villajoyosa, seven miles from the coastal resort of Benidorm. The Spanish government has so far refused to confirm that the remains are Kuzminov, but the paper said he was identified via his fingerprints.

Earlier this week, Russia’s SVR foreign intelligence service, praised the former soldier’s death but refused to confirm any involvement by Russian authorities. The Ukrainian intelligence service is so far the only official confirmation that the body belongs to that of Kuzminov.

Kuzminov made headlines last summer when he flew his Mi-8 helicopter from the a base in Russia to Kyiv, where he was warmly welcomed. He said he took the action to protest what he said was an unjust war against Ukraine and encouraged other Russian soldiers to do the same.

Spanish intelligence sources told El Pais that the only question remaining is whether the killing was carried out by the SVR or another agency such as the FSB security service or Russia’s GRU intelligence agency. The paper quoted a Spanish diplomatic source as saying the incident was “very serious” and that Spain would “respond forcefully” if Moscow’s involvement was confirmed.