21 December 2015 :

Three quarters of American executions in 2015 involved cases of "crippling disabilities and uncertain guilt," according to a report by the Charles Hamilton Houston Institute for Race and Justice at Harvard University.
Saying that the 2015 executions revealed "a broken capital punishment system," the report found that, "of the 28 people executed in 2015, 75% were mentally impaired or disabled, experienced extreme childhood trauma or abuse, or were of questionable guilt." It said seven people who were executed suffered from serious intellectual impairment or brain injury, including Warren Hill, who even the state's doctors agreed had intellectual disability, and Cecil Clayton, who lost 20% of his prefrontal cortex as a result of a sawmill accident. An additional seven suffered from serious mental illnesses. One, Andrew Brannan, was a decorated war veteran whom the Veterans Administration had classified as 100% disabled as a result of combat-related Posttraumatic Stress Disorder from his service in Vietnam.
The report identified five more cases in which the executed prisoners had experienced extreme childhood trauma and abuse, and another two - Lester Bower and Brian Keith Terrell - in which it said the executed men "were potentially innocent."