Nikita Tikhonov and his companion and accomplice, Yevgeniya Khasis, were convicted of the murders April 28, RIA Novosti reported. Khasis was sentenced to 18 years in prison.
Lawyer Stanislav Markelov and Anastasia Baburova, a reporter for the liberal Novaya Gazeta newspaper, were shot dead in broad daylight in downtown Moscow in January 2009. Investigators said Baburova was killed because she witnessed Markelov's death.
Both Tikhonov and Khasis are linked to Russky Obraz, a banned extreme nationalist group.
Tikhonov admitted an arms trading charge but denied the killing.
Tikhonov also must pay Baburova's parents 2,040,000 rubles ($74,500) in damages.
Defense lawyers promised to appeal.
"This is a premeditated murder, a politically charged murder," said Ludmila Alekseyeva, leader of the Moscow Helsinki Group, a human rights watchdog.
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