In the sentencing phase of capital cases, mitigating evidence can be the deciding factor in whether a defendant gets life without parole or the death penalty. The U.S. Supreme Court has defined mitigating evidence as any feature of a defendant's character or history, or characteristics of the offense, that may convince the fact-finder to impose a sentence less than death (Lockett v. Ohio, 1978). The court has also held that all relevant mitigating evidence must be considered by the sentencer (Eddings v. Oklahoma, 1982).
Defense attorneys in capital cases are required to conduct an investigation of all reasonably available mitigating evidence to satisfy the Sixth Amendment's guarantee of effective counsel (Wiggins v. Smith, 2003). Yet evidence suggests this often does not happen. That is why most capital appeals are based on claims of ineffective assistance of counsel. However, not only is it more difficult for capital defendants to win on appeal, but the standard for ineffective assistance of counsel is difficult to satisfy because a defendant must show that counsel's performance was deficient and there is a reasonable probability that the trial outcome would have been different if the counsel had been better.
Several Supreme Court cases shed light on what qualifies as ineffective counsel in capital cases. In Williams v. Taylor (2000), the court found that an attorney did not conduct a thorough background investigation of his client because he failed to introduce evidence in the defendant's favor. In Rompilla v. Beard (2005), defense counsel knew that the prosecution relied on the defendant's conviction file, but failed to examine it. The court held that defense counsel had a duty to make reasonable efforts to review all evidence that the attorney knows the prosecutor will likely use as aggravating evidence. And in Porter v. McCollum (2009), the court found ineffective assistance of counsel when the defense attorney presented no evidence of the defendant's history of childhood abuse, brain abnormality or cognitive deficiencies.
To satisfy their obligation of conducting a life history of a capital defendant, attorneys often hire mental health experts to perform mitigation evaluations. These experts rely on social science research and scholarship to guide them through mitigation assessments in capital cases. The science is also useful for attorneys who are seeking guidance on how to conduct mitigation investigations (DeMatteo, Murrie, Anumba, & Keesler, 2011; Heilbrun, DeMatteo, Holliday, & LaDuke, 2014).
Mitigation evaluations differ from other types of forensic mental health assessments in that they require a thorough biographical examination of the experiences, life stages and capabilities that may have affected a defendant's life course. Mitigation evaluations are comprehensive in scope and therefore often lengthy, typically involving multiple interviews and a review of all available records. As a result, mitigation evaluations may span over the course of weeks or even months to ensure that sufficient attention is given to the defendant's history.
Despite being retained by the defense, mitigation evaluations must be objective and based on a thorough understanding of how certain factors may be mitigating. Forensic mental health professionals must understand how developmental factors (such as early childhood abuse), criminogenic factors and clinical factors affect an individual's risk level. An examination of protective factors, such as social support, education and resilient personality traits, is also important because these factors may buffer the effect of risk factors.
It is important that attorneys and mental health experts work together in capital cases, while recognizing their individual expertise, roles and professional boundaries. The use of mental health experts in capital cases can be an effective way for attorneys to satisfy the Sixth Amendment's requirement of effective assistance of counsel, and for capital defendants to receive a more informed disposition from the sentencer.
