Self-declared prophet Pyotr Kuznetsov established his True Russian Orthodox Church after splitting from the official Russian church.
Kuznetsov, who blessed his followers and sent them into the cave earlier this month, did not join them himself.
He was undergoing psychiatric evaluation on Friday, a day after he was charged with setting up a religious organisation associated with violence, Guseynov said.
Russian state television broadcast footage of Kuznetsov, a thin, bearded man, speaking at the clinic where he was being examined.
Kuznetsov said cult members initially wanted to dig small shelters where they could spend a day or two in prayer, but that later they "had the idea of making a big dugout for all of us to go to and stay there, just to avoid acts of hooliganism by the local population".
The 29 people, including four children, one only 18 months old, had stocked the cave with food and other supplies.
Kuznetsov said in the footage, shown on Rossiya TV channel, that he had not gone into the cave himself because "I had to meet others who were yet to arrive".
On Thursday, Russian Orthodox monks carefully tried to make contact with the cult, but members inside the cave refused to speak with clergy.
The Russian newspaper Izvestia said most of the adults in the cave were women.
Kuznetsov, 43, an engineer who comes from a deeply religious family, declared himself a prophet several years ago, left his family and settled in the village of Nikolskoye.
He began writing books, drawing upon a mixture of established beliefs as he visited monasteries in Russia and Belarus and sought new followers, Guseynov said.
Kuznetsov said his group believed that in the afterlife they would be judging whether others deserved heaven or hell, Izvestia reported Friday.
Followers of his group were not allowed to watch television, listen to the radio or handle money, media reports said.
Alexander Dvorkin, of the Moscow-based independent Centre of Religious Studies, said Kuznetsov's followers were in serious danger and "any wrong move" by authorities could cost lives.
"Their minds are being manipulated, they are under the strong influence of their leader," Dvorkin said.
He said there were about 10 similar cults in Russia and that, so far, authorities have done little or nothing about them.
Georgy Ryabov, a spokesman for the Russian Orthodox Church, said the emergence of Kuznetsov's cult was a consequence of "the absence of a system of spiritual and moral education" in Russia.
"All Christians of Russia have to pray for them so they awaken and understand their mistake," Ryabov said.