The court sentenced the gang leader, Ali Kaitov, to 17 years in a high-security prison, giving his 15 accomplices various terms of imprisonment from eight-and-a-half years to life.
The court press secretary said the defendants were proved guilty beyond a reasonable doubt, adding the sentences may be appealed within 10 days at the Supreme Court of Russia.
The bodies of seven residents of Karachayevo-Cherkessia - regional lawmaker Rasul Bogatyryov and six of his friends, who disappeared in the early hours of October 11, 2004, were found in an abandoned mine near the village of Kumysh, Karachayevsk district.
Their relatives said they had headed for the out-of-town house of Ali Kaitov, chairman of OAO Kavkaz-Tsement and son-in-law of the president of Karachayevo-Cherkessia. Witnesses said they had heard bursts of automatic fire near the house later for about half an hour.
Kaitov was arrested on October 25, 2004, while other suspects were arrested later.
The "Kaitov case" sent shock waves throughout the republic, leading to mass riots with relatives of those killed seizing the government building and demanding the resignation of the republic's president and senior law enforcement officials.