What is the state of the mental state of a defendant in a murder case?

the victim's mental state prior to the killing. A rational trier of fact may disbelieve those portions of a defendant's statements that are obviously self-serving, reject implausible explanations, and draw inculpatory inferences from his testimony and the other evidence. ( People v. Silva (2001) 25 Cal.4th 345, 369, 106 Cal.Rptr.2d 93, 21 P.3d 769.) It would have been reasonable for the jury to conclude defendant lacked credibility or otherwise reject his account of the events and his claim of self-defense.