Chapter 5. Weight Of Evidence Generally of California Evidence Code >> Division 3. >> Chapter 5.

As used in this chapter, "direct evidence" means evidence that directly proves a fact, without an inference or presumption, and which in itself, if true, conclusively establishes that fact.
Except where additional evidence is required by statute, the direct evidence of one witness who is entitled to full credit is sufficient for proof of any fact.
If weaker and less satisfactory evidence is offered when it was within the power of the party to produce stronger and more satisfactory evidence, the evidence offered should be viewed with distrust.
In determining what inferences to draw from the evidence or facts in the case against a party, the trier of fact may consider, among other things, the party's failure to explain or to deny by his testimony such evidence or facts in the case against him, or his willful suppression of evidence relating thereto, if such be the case.