MOSCOW—A retired Russian military intelligence colonel has been found guilty of leading a bizarre plot that envisioned a group of elderly people taking over the government.

Prosecutors say Vladimir Kvachkov, 64, organized a group who planned to seize power by training crossbow-wielding men to seize military depots and then descend upon Moscow with tanks.

Moscow City Court on Friday sentenced him to 13 years in prison for attempting to organize an armed uprising. A retired police captain, 62-year-old Alexey Kiselev, was sentenced to 11 years as a co-conspirator.

Kvachkov, who denied the charges, became a nationalist folk hero after twice being acquitted for a 2005 assassination attempt on former deputy prime minister Anatoly Chubais, the mastermind of Russia's 1990s privatization drive.