A young nationalist was sentenced to life in prison, Russia’s most stringent punishment, on Friday for fatally shooting a human rights lawyer and a young journalist two years ago on a busy street near the Kremlin. His common-law wife, who prosecutors said acted as a lookout, was sentenced to 18 years as an accomplice. The sentence brings to a close a case that deeply shook Russian human rights circles, which have been dogged by a series of high-profile killings. Last week, the couple, Nikita Tikhonov, 30, and Yevgenia Khasis, 26, were found guilty. Defense lawyers appealed the sentence on Friday, saying the judge had sided with prosecutors. “This can be qualified in whatever way you like, a costume ball, a farce, a reprisal, but not a trial,” Aleksandr Vasilyev, Mr. Tikhonov’s lawyer, told the Interfax news service.