In 2015, America had the lowest number of executions in 25 years, according to a new report released by Harvard Law School’s Charles Hamilton Houston Institute for Race & Justice.

But of the 28 people executed, 68% suffered from severe mental disabilities or experienced extreme childhood trauma and abuse. A significant number of the executed individuals had multiple mental impairments. Two individuals were executed despite doubts about their guilt, according to the report.

Charles Ogletree, director of the Charles Hamilton Houston Institute for Race & Justice, noted, “It is deeply troubling that half of the people that our nation executed this year had mental impairments or brain injuries that made them functionally equivalent to individuals whom the U.S. Supreme Court has deemed inappropriate for execution, including persons with intellectual disabilities and juveniles.”

“Executing individuals who suffer from crippling mental illnesses, brain injuries, and debilitating childhood trauma crosses a moral line that defines civilization,” said David Harris, managing director of the Institute. “If after nearly 40 years we haven’t been able to devise a death penalty system that can accurately distinguish the innocent from the guilty, or the mentally disabled from the most culpable offenders, we shouldn’t have a death penalty at all. Executing innocent people, as well as those with crippling mental disabilities, serves no legitimate purpose.”

The report also noted that a majority of states have essentially abandoned the death penalty in law or in practice. A total of thirty-three jurisdictions—30 states along with the District of Columbia, the federal government, and the U.S. military—have either formally eliminated the death penalty or have not carried out an execution in the last nine years.

Death sentences also declined in 2015. In Texas—the state most associated with capital punishment—the annual number of death sentences fell from a high of 48 in 1999 to just two sentences confirmed by judges in 2015, a 96% decrease. Nationwide, in the six-year period between 2010 and 2015, just 10 counties imposed six or more death sentences.

For more information:

Death Penalty 2015 Year End Report

Death sentences, executions plummeted in 2015