I'd say this is less on the ability of Russian assassin's and more on this guy for reaching out to his girlfriend back in Russia.

In Spain, Mr. Kuzminov lived “an indiscreet life,” the senior Guardia Civil official said. He went to bars popular with Russian and Ukrainian clientele, burning through the money he had received from the Ukrainian state. He drove around Villajoyosa in a black Mercedes S-Class.

Exactly how the killers found him has not been established, though two senior Ukrainian officials said he had reached out to a former girlfriend, still in Russia, and invited her to come see him in Spain.

“This was a grave mistake,” one of the officials said.