With a special court's permission, agency officials recorded Singh's statement at a Rohtak prison where he is serving 20-year jail term for raping two sadhvis yesterday, CBI sources said.
The Central Bureau of Investigation (CBI) had registered the case in January, 2015, on the orders of the Punjab and Haryana High Court.
The FIR was registered against Singh and others under various charges, including criminal conspiracy for voluntarily causing grievous hurt by dangerous weapons or means, for alleged castration of 400 devotees at the Sirsa-based Dera.
The official had said the petitioner, Hansraj Chauhan, has alleged that around 400 male devotees belonging to many states including Haryana, Punjab and Rajasthan were castrated at the Dera headquarters after its head falsely claimed that the "castration would lead to realisation of God through him".