The Supreme Court's criminal chamber on December 8 ruled that the sentences were fair and dismissed claims that the three men were killed upon orders from state officials.
Sarsenbaev's friends believe the sentences serve to cover up a contract political killing.
Naghiz Ak Zhol leader Tolegen Zhukeev told RFE/RL's Kazakh Service today that lawyers for his party and Sarsenbaev's family will appeal to the Supreme Court's higher chamber, but without high hopes.
"The [Supreme] Court will continue hearing the case," he said. "So far only its criminal collegium has heard the case. Unfortunately we don't have great hopes. I don't think the case will be examined the way we would like it to be [because] is clear that a thorough investigation would lead to scandalous findings."
A regional court on August 31 sentenced former security officer Rustam Ibragimov to death on charges of planning and carrying out the assassination of Sarsenbaev, his bodyguard, and his driver. The sentence will not be carried out as long as Kazakhstan maintains its moratorium on executions.
Another nine people received jail terms of between three and 20 years. The defendants claim they confessed under duress.
(with material from Interfax-Kazakhstan)