At the start of the trial May 13, Ali Taziyev, an ethnic Ingush also known as Magas, pleaded guilty to illegal weapons possession and the organization of an illegal armed group.
He pleaded not guilty to taking part in terrorist acts that killed 26 and injured 344 people.
Taziyev was arrested in 2010 and has been charged with involvement in 24 terrorist-related incidents.
He is accused of masterminding and organizing the attempted assassination in 2009 of Yunus-Bek Yevkurov, the leader of Russia's Republic of Ingushetia.
Umarov unilaterally declared an independent Islamic state in the North Caucasus in 2007 and later appointed Taziyev as his top military commander.