where in most of his devices, he created the circuitry. and it was not through a timer like many bombers use. he actually took the time to create the mechanism to create the circuits. and that made it really difficult for investigators. >> he built his own switches for the bombs from hickory. and when he bought batteries, he would peel off the covers of the batteries so we wouldn't be able to go back and trace where those batteries might have been purchased. >> there was no evidence that would lend itself to take us to a particular manufacturer, vendor, sales documents, a person's name on a purchase order. there wasn't anything like that connected with the devices. >> but as the attacks continued, the bombs became more sophisticated. and more lethal. may 1982. a pipe bomb mailed to the head of the computer department at vanderbilt university in nashville explodes when it's opened by a secretary.