see - sc.judiciary.gov.ph/jurisprudence/2013/july2013/197537.pdf
"x x x.
The fact of AAA’s mental retardation did not impair the credibility of her testimony. Mental retardation per se does not affect credibility. A one
mentally retarded may be a credible witness. The acceptance of her
testimony depends on the quality of her perceptions and the manner she can make them known to the court.23
We have thoroughly examined AAA’s testimony and found no reason
to depart from the legal adage that this Court accords the trial judge’s
assessment of the credibility of witnesses great respect in the absence of any attendant of grave abuse of discretion on the account that the trial court had the advantage of actually examining both real and testimonial pieces of evidence, including the demeanor of the witnesses, and is in the best position to rule on the matter. The rule finds an even greater application when the trial court’s findings are sustained by the Court of Appeals.24
Taking into consideration the positive and categorical declaration of
AAA and the medical findings to support her claims, we affirm the lower
courts’ unanimous finding that AAA , by proof beyond reasonable doubt,
was raped by the appellant.
Appellant’s denials and alibi cannot prevail over the positive, consistent and straightforward testimony of AAA. Alibi is an inherently weak defense because it is easy to fabricate and highly unreliable. To merit approbation, the accused must adduce clear and convincing evidence that he was in a place other than the situs criminis at the time the crime was committed, such that it was physically impossible for him to have been at
the scene of the crime when it was committed.25 Appellant admitted that he was in fact with AAA at his house when the rape incident occurred.
Considering that he was at the place where the crime was committed, his
alibi cannot be given any weight or value.
x x x."
