There used to be a well-established practice, when, due to the lack of "direct indication of something" in the law, explanations of the Plenum of the Supreme Court of the USSR (RSFSR) were periodically issued on certain nuances of judicial practice, on which law enforcement officers relied in their law enforcement activities ...
And appropriately documented opinions (conclusions, materials, etc.) of detectives can be used as testimony of specialists in the process of preliminary and judicial investigation ...