POTTAWATOMIE COUNTY, Oklahoma - Attorneys for a man found guilty of murdering a police officer are trying to save their client from the death penalty. 

Wednesday, public defenders for Byron Shepard called Dr. Antoinette McGarrahan, a forensic psychologist from the University of Texas.

She told jurors, she reviewed the convicted killer’s medical, school, and criminal records and interviewed Shepard for eight hours at the Pottawatomie County Jail.

McGarrahan testified Shepard suffers from depression, mental impairment from drug use, traits of antisocial personality disorder and impaired cognitive function. She told jurors he allegedly scored near the intellectual disability range on an IQ test.

Assistant District Attorney Pattye High questioned the expert over basing many of her opinions on defense summaries of witnesses statements, instead of talking to Shepard’s friends and family herself.

She also raised questions about the $16,000 being paid for McGarrahan’s expert testimony.

A childhood psychologist, also hired by the defense, told jurors Shepard’s childhood gave him “PTSD” from “toxic exposure.”

Prosecutors argue the expert’s report failed to include details about Shepard being raised by his grandparents.