Robyn Anderson, an 18-year-old Columbine High senior, bought  three on a weekend shopping spree with her 17-year-old companions.  Klebold and Harris supplied the cash, she the driver's license.  The assault weapon, a TEC-DC9, was sold at a different gun show to  Mark Manes, a young man who later resold it for $ 500 to the  killers - and then sold them a fresh supply of ammunition on April  19, 1999