Kuzminov's escape and cooperation with Ukrainian intelligence was widely publicised.
ADVERTISEMENTA week ago, a body was found in a car park in La Villajoyosa, Spain. The man, who had been shot to death, was identified as a Ukrainian national.
But after days of investigation, the police learnt that he was in fact Maxim Kuzminov, a Russian pilot who defected with his Mi-8 helicopter and surrendered to the Ukrainian army last August.
His identity was confirmed by fingerprints, as the documents he was carrying were false.
In addition to Spain's Guardia Civil, Ukrainian military intelligence spokesman Andriy Yusov confirmed the former Russian soldier's death on Monday.
Kuzminov's escape and cooperation with Ukrainian intelligence were widely publicised.
The story served as propaganda for the country's war effort: A triumph for Ukraine and a blow to Russia.
Alarm bells went off when a Russian Mi-8 military transport helicopter landed in Ukraine last summer. Ukrainian intelligence claimed at the time that the operation was not part of the Russian invasion, but had been coordinated by them.
Also on board were two Russian soldiers who were unaware of the pilot's plan. Both died after landing in Ukraine, according to sources quoted by Pravda.
Before the plane's final destination was known, Russian bloggers had reported its disappearance, but claimed it was due to the pilot's disorientation.
The pilot planned to bring as large an arsenal of weapons as possible to Ukraine.
In return, the Russian pilot's family was transferred to Ukraine to live with him. He was also offered new documents and compensation of half a million dollars.
Kuzminov graduated from the Sizran aviation school in southern Russia, but had never wanted to fight in the Ukraine war.
"I regret what is happening, the killings, the tears, the blood," he said in a statement.
"I don't want to be an accomplice to Russian crimes," he added.
When Ukrainian intelligence contacted him and proposed the plan, Kuzminov was reluctant. But he decided to take the risk and flew his helicopter extremely low to avoid radar detection.
The pilot explained that for a few days no one in Russia knew where the helicopter was until it landed in Ukraine.
The head of Russia's foreign intelligence service, Sergei Narishkin, claimed that Kuzminov was a "criminal traitor" and had been a "moral corpse since he planned the dirty crime'" according to the official Russian news agency RIA Novosti.
It is not known who killed Kuzminov.