What is the standard of proof in a criminal case?

proffered proof in a criminal case depends upon whether or not it tends to sustain a legitimate hypothesis of the guilt of the defendant and, generally speaking, an incidental fact is relative to the main fact in issue when, in accord with the ordinary course of events and common experience the existence of the incidental fact, standing alone or when considered in connection with other established facts, tends in some degree to make the main fact in issue certain. It is not necessary that such incidental fact should bear directly upon the main fact in issue, for it will suffice as a pertinent piece of proof if it can be said to constitute a link, however small, in the chain of evidence, and tends thereby to establish the existence of the main fact in issue. [Citation.]" (People v. Billings (1917) 34 Cal.App. 549, 552-553.) The strength of such tendency, or the amount of such weight, is to be determined by the jury. (Moody v. Peirano (1906) 4 Cal.App. 411, 418.)