Lawyers defending accused theater gunman James Holmes challenged the reliability of firearms analysis on Wednesday, despite conceding that their client was solely responsible for the 2012 massacre that killed 12 moviegoers.
In a hearing before Arapahoe County District Court Judge Carlos Samour, public defenders sought to have expert ballistics testimony precluded from the onetime neuroscience graduate student's murder trial.
Dale Higashi, an agent with the Colorado Bureau of Investigation, said all the bullet fragments and shell casings that he analyzed from the crime scene could be traced to three of the weapons belonging to Holmes.
Defense lawyers argued that firearms analysis is subjective, and not based on quantifiable scientific fact.
Holmes, 26, has pleaded not guilty by reason of insanity to opening fire inside a suburban Denver cinema in July 2012 during a midnight screening of the Batman film "The Dark Knight Rises."
The rampage killed 12 moviegoers and wounded 70 others.
Prosecutors have charged Holmes with multiple counts of first-degree murder and attempted murder, and said they will seek the death penalty if he is convicted.
After invoking the insanity defense, Holmes underwent a court-ordered sanity examination last year, but the conclusions have not been made public.
His lawyers have said that Holmes was experiencing a psychotic episode when he went on the shooting spree.
In February, Samour ordered a second sanity evaluation after siding with prosecutors who argued that the initial examination was deficient.
Shackled and clad in red prison garb, Holmes sat impassively throughout the hearing, and did not appear to acknowledge his parents who were in the courtroom.
Former Denver prosecutor and legal analyst Craig Silverman said Holmes' lawyers are contesting all the evidence amassed against their client in a bid to spare him from execution.
"This is another sideshow designed to create an appellate issue," Silverman said.
Samour gave no indication on Wednesday on when he will rule on the defense motions.
Jury selection is set to begin on begin on Dec. 8.