Judge Mary Staley set a May 28 trial date for 63-year-old Jesse James Warren of Temple.
Lawyers for Warren filed court papers contending that he was insane at the time of the Jan. 10, 2010, shootings, according to reports.
Cobb County police said a gunman first confronted someone in the parking lot at the Penske Truck Rental facility in the Kennesaw area before moving to the truck bay area, shooting victims along the way.
Jaider Felipe Marulanda of Lawrenceville; Robert Gonzalez of Dallas, Ga.; and Van Springer of Woodstock, were killed.
Warren, who had previously worked at Penske Truck Rental for four years, pleaded not guilty in 2010 to 16 counts, including three counts each of malice murder, felony murder and aggravated assault, two counts of aggravated battery and five counts of possession of a firearm during the commission of a crime, in spring 2010.
Prosecutors said Warren burst into the office wearing camouflage and unloaded his handgun into a crowd of former colleagues as the office was bustling with some two dozen workers and several customers. When the attack was over, three people were dead — two employees and a customer — and two more were in critical condition, according to authorities.
After the shootings, prosecutors say Warren sped away in a pickup truck and was arrested by authorities about a mile away.
Warren was a former employee of the truck rental business. Warren worked at Penske from June 2005 until July 2009.