Sir Alfred Wills in his admirable book "Wills' Circumstantial Evidence"

Lays down the following rules specially to be observed in the case of circumstantial evidence:
(1) The facts alleged as the basis of any legal inference must be clearly proved and beyond reasonable doubt connected with the factum probandum;
(2) The burden of proof is always on the party who asserts the existence of any fact, which infers legal accountability;
(3) In all cases, whether of direct or circumstantial evidence the best evidence must be adduced which the nature of the case admits;
(4) In order to justify the inference of guilt, the inculpatory facts must be incompatible with the innocence of the accused and incapable of explanation, upon any other reasonable hypothesis than that of his guilt,
(5) If there be any reasonable doubt of the guilt of the accused, he is entitled of the right to be acquitted.