Vidado Dumlao (defendant) shot and killed his mother-in-law. At trial, Dumlao’s expert witness testified that Dumlao suffered from a paranoid personality disorder, which included pathological jealousy concerning his wife. Dumlao’s trial testimony regarding his perceptions of the night of the shooting confirmed the extreme nature of his jealousy. Dumlao asked the trial court to instruct the jury that it could find him guilty of manslaughter if it found sufficient evidence to support the conclusion that he acted under the influence of extreme mental or emotional disturbance for which there was a reasonable explanation. The court refused to give the requested instruction. The jury convicted Dumlao of murder. Dumlao appealed.