Sanatan Santha is a militant Hindutva group active in Maharashtra and Goa, closely linked with the Hindu Janajagruti Samiti. It claims to be a spiritual organisation but is widely associated with various acts of terrorism, and the murder of prominent rationalists.
In 2011 two members of the group were convicted of bombing theatres in Maharashtra, apparently to protest against plays offensive to Hinduism. They were later granted bail. Jayant Balaji Athavale, the founder of the organisation called such acts "a sacrifice". Another Sanstha member is wanted in relation to bombings in Madgaon (Goa), and has been named as the prime suspect in the murder of rationalist Govind Pansare. The Sanstha also been linked to the murders of Kannada academic and rationalist M. M. Kalburgi, and of anti-superstition campaigner Narendra Dabholkar..
There is evidence from former members that the Sanstha functions as a cult. According to the Goa police, it is involved in brainwashing and sexual exploitation. Sanatan Sanstha enjoys the support of the Shiv Sena.
References: Sanatan Sanstha on Communalism Watch and Narendra Modi Facts.