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
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
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. n
• DeMatteo, D., Murrie, D. C., Anumba, N. M., & Keesler, M.
E. (2011). Forensic mental health assessments in death penalty
cases. New York, NY: Oxford University Press.
• Heilbrun, K., DeMatteo, D., Holliday, S. B., & LaDuke, C.
(Eds.). (2014). Forensic mental health assessment: A casebook
(2nd ed.). New York, NY: Oxford University Press.
A matter of life or death
Mental health experts play a key role in evaluating the mitigating
evidence that informs a defendant’s sentence.
By Alice Thornewill, Rachel Bomysoad and David DeMatteo, JD, PhD, Drexel University