Padala Veera Reddy v. State of A.P. and Ors. AIR 1990 SC 79

it was laid down that when a case rests upon circumstantial evidence, such evidence must satisfy the following tests:
(1) The circumstances from which an inference of guilt is sought to be drawn, must be cogently and firmly established;
(2) Those circumstances should be of a definite tendency unerringly pointing towards guilt of the accused;
(3) the circumstances, taken cumulatively should form a chain so complete that there is no escape from the conclusion that within all human probability the crime was committed by the accused and none else; and
(4) The circumstantial evidence in order to sustain conviction must be complete and incapable of explanation of any other hypothesis than that of the guilt of the accused and such evidence should not only be consistent with the guilt of the accused but should be inconsistent with his innocence.