Lotter, 46, has maintained his innocence in the Dec. 31, 1993, killings at a Humboldt farmhouse, despite being convicted of three counts of first-degree murder. He's spent the past 22 years on death row pending appeals.

Late last week, Rebecca Woodman of the Death Penalty Litigation Clinic in Kansas City, Missouri, let a Nebraska federal judge know about a post-conviction motion filed in Richardson County alleging Lotter is an "intellectually disabled person."

In a 60-page motion, she and two other attorneys representing Lotter raised numerous arguments, the newest among them challenging that Lotter is ineligible for the death penalty given recent IQ testing.

The attorneys cited a landmark 2002 U.S. Supreme Court decision forbidding the execution of people with intellectual disabilities and a later decision by the court in 2014 rejecting a strict IQ cutoff rule in Florida.

In Nebraska, by law, an IQ of 70 or below is presumptive evidence of an intellectual disability.

According to the court filing last week, Dr. Ricardo Weinstein, a clinical and forensic neuropsychologist from Encinitas, California, evaluated Lotter last year and determined he scored a 67 for general intellectual ability on the Woodcock-Johnson test, the equivalent IQ of an average 8-year-old.

In 1981, at the age of 10, Lotter scored a 76, which adjusts to a 73 under today's scoring, according to the expert.

Attorney Tim Noerrlinger said Weinstein also reviewed trial records and school records showing Lotter was in special-education classes, and he interviewed Lotter's mother, foster mother, a psychiatrist who worked with Lotter as a child and others before determining that Lotter had significant adaptive deficits.

It's Weinstein's opinion that Lotter qualifies for the diagnosis of intellectual developmental disability.

But that ultimately will be a decision for the court.

Lotter's attorneys pointed to the Florida decision, where the Supreme Court found that professionals have long agreed an IQ test score should be read not as a single number but as a range, which can fluctuate for several reasons.

If Richardson County District Judge Vicky Johnson grants an evidentiary hearing to consider the issue or others raised by Lotter's attorneys, the state would be allowed to seek its own experts.

Lotter was sentenced to death for his role in the 1993 killings of Brandon Teena and two witnesses, Lisa Lambert and Philip DeVine. Thomas Nissen is serving life sentences for the part he played in the crime.

Nebraska's death row inmates