When will a jury consider a defendant's mental state during the guilt and sentencing phases of their trial?

During "the guilt phase, a defendant's mental state is directly relevant for limited purposes-principally, . . . legal insanity or actual failure to form the requisite intent at the time of the offense." Bemore v. Chappell, 788 F.3d 1151, 1171 (9th Cir. 2015). By contrast, at sentencing, the jury has wide "latitude to consider amorphous human factors," id. (citation omitted); thus, "[i]t is imperative that all relevant mitigating information be unearthed for consideration at the capital sentencing phase." Id. (quoting Wharton v. Chappell, 765 F.3d 953, 970 (9th Cir. 2014)). "To that end, trial counsel must inquire into a defendant's social background, family abuse, mental impairment, physical health history, and substance abuse history; obtain and examine mental and physical health records, school records, and criminal records; consult with appropriate medical experts; and pursue relevant leads." Id. (internal quotation marks and citation omitted). "Where counsel is aware of potentially mitigating evidence, he or she must investigate that evidence, absent a reasonable strategic reason not to do so." Id. (citation omitted).