Duncan's attorneys argue that their client wasn't mentally competent during his trial and successfully had Ducan's three death penalty sentences overturned. The 9th U.S. Circuit Court of Appeals ruled in July 2011 that Duncan should have been given a competency hearing before he was allowed to waive his appeal.
In preparation for the January competency hearing, U.S. District Court Judge Edward Lodge has approved the defense's request to use an expert in the diagnosis of mental disorders. Duncan's defense is expected to call Dr. Michael First, an expert in the Diagnostic and Statistical Manual of Mental Disorders, a text medical professionals regularly use to diagnose mental illness.
But federal prosecutors are hoping to call another expert, Dr. Ronald Roesch, the director of the Mental Health, Law and Policy Institute at Simon Fraser University, who examined Duncan earlier this year.
Duncan's competency hearing will focus only on the crimes he committed against the Idaho children, though Duncan has now been convicted of five different murders in three states.