Complex sentence: The documents about the rebellion were found by the local ethnographer Boris Sennikov in 1982 that he found while cleaning the altar from the sand in the Winter Church of the Kazan monastery in Tambov.
Split into simpler sentences: The documents about the rebellion were found by the local ethnographer Boris Sennikov in 1982. He found while cleaning the altar from the sand in the Winter Church of the Kazan monastery in Tambov.