Crusius, 24, drove from his home in Dallas to the border city of El Paso and opened fire at a Walmart on Aug. 3, 2019, in what prosecutors described as a racist attack.
FILE PHOTO: Walmart shooting suspect Patrick Crusius appears in court in El Paso, Texas. (Briana Sanchez / El Paso Times via AP, Pool, File)
He had posted a manifesto online that said the shooting was "in response to the Hispanic invasion of Texas," and told police after surrendering that he was targeting Mexicans, according to an arrest warrant.
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His attorneys wrote in court filings that Crusius "has been diagnosed with severe, lifelong neurological and mental disabilities," which they argued should be a "red flag" for prosecutors considering whether to pursue the death penalty.
Shooting suspect Patrick Crusius, charged with capital murder for a mass shooting at a Walmart store in El Paso, is seen in this police photo released from El Paso, Texas, U.S., August 5, 2019. (El Paso Police Department/Handout via Reuters)
Crusius has pleaded not guilty to separate state capital murder charges in Texas, where he could still face the death penalty if convicted.
Former El Paso County District Attorney Yvonne Rosale resigned last November amid criticism that her office was slowing down Crusius' prosecution.
People hug beside a makeshift memorial outside the Cielo Vista Mall Wal-Mart where a shooting left 23 people dead in El Paso, Texas. (Mark Ralston/AFP via Getty Images)
Crusius will be sentenced later this year and faces life in prison for each of the 90 federal charges he pleaded guilty to on Wednesday.
The Associated Press contributed to this report.