P.R. Laws Ap. tit. 32A, § IV, Rule 10
The court or the trier of facts shall weigh the evidence introduced in order to determine which facts have been established or proven, subject to the following principles:
(A) The burden of proof is on the party who would be defeated if no evidence were introduced by either side.
(B) The burden of producing evidence is, first of all, upon the party holding the affirmative of the issue.
(C) To establish a fact, the degree of proof required is not that which, excluding the possibility of error, produces absolute certainty; the only requirement is moral certainty or conviction upon an unprejudiced mind.
(D) Direct evidence from a witness who deserves full credit is sufficient proof of any fact, unless otherwise provided by statute.
(E) The court or jury is not bound to decide in conformity with the declarations of any number of witnesses which do not produce conviction in their minds, against a lesser number of witnesses or against other evidence convincing to their minds.
(F) In civil cases, the trier’s decision shall be in accordance with the preponderance of evidence on the basis of probability; in criminal cases, guilt must be established beyond a reasonable doubt.
(G) When it seems that a party offers evidence that is weaker and less satisfactory than the one it could have offered, the evidence introduced should be viewed with distrust.
(H) Any fact in controversy may be established through direct, indirect or circumstantial evidence. Direct evidence is that which proves the fact in controversy without inference or presumption and which, if true, establishes the fact conclusively. Indirect or circumstantial evidence is that which tends to establish the fact in controversy by proving another one from which-together with other established facts-one could reasonably infer the fact in controversy.