Section 656(a) in Police Regulations, Bengal , 1943
(a)Experts may be cited as witnesses to prove previous convictions of undertrial prisoners only when the ordinary methods fail, but they shall not be so cited by subordinate police officers without the sanction of the Superintendent. An expert can only prove identity under sections 45 and 73 of the Indian Evidence Act, 1872, while jail warders, police officers and complainants and witnesses in previous cases can prove both identity and previous convictions.
