Judge Mary Staley set a May 28 trial date for 63-year-old Jesse James Warren of Temple.
The Atlanta Journal-Constitution reports that lawyers for Warren filed court papers contending that he was insane at the time of the Jan. 10, 2010, shootings.
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.
Joshua B. Holbrook of Rome was also wounded in the shooting.