A mental-retardation determination would make defendant Joshua Steven Durcho, 28, ineligible for the death penalty on the five counts of first-degree murder, The Oklahoman reported.
Durcho was charged after his girlfriend and her four young children were found dead in their El Reno apartment 25 miles west of Oklahoma City in January 2009. Prosecutors allege Durcho strangled Summer Rust, 25, because she threatened to call police on him and he vowed he would never go back to prison.
At the time of the deaths, there were warrants out for his arrest in a drunken-driving case and a methamphetamine case.
Prosecutors allege Durcho strangled Rust's three daughters -- Kirsten Rust, 7, Autumn Rust, 7, and Evynn Garas, 3 -- and her son, Teagin Rust, 4, to eliminate them as witnesses.
His lawyers told Canadian County District Judge Gary Miller in July that Durcho scored a 72 on an IQ test administered by a psychologist. The psychologist recommended Durcho get a medical scan because of a possible organic brain injury, they said.
Miller ruled Durcho could be assessed by a nationally recognized expert.
Under Oklahoma law, mental retardation is defined as an IQ score of 70 or less, along with "significant limitations in adaptive functioning." The impaired functioning must have appeared before the defendant's 18th birthday.
The lawyers told Miller they had records showing Durcho was in special-education classes before he dropped out of school after the eighth grade.