The same person or persons constructed all IED's used in the bombings by using wooden components, improvised dowel-type initiators, and antidisturbance fusing mechanisms. All but one device used household-type batteries, lamp cords, and pipe bombs. The Federal Bureau of Investigation (FBI) directed the bombing investigations, captioning its efforts UNABOM to reflect the university and airline targets. Bombing incidents in 1993 targeted a medical scientist and a computer scientist. The IED's in both incidents were assembled almost identically. They were pipe bombs filled with a low-explosive powder contained in a homemade wooden box which was glued to the inside of a padded envelope. The devices were constructed with electrical wire, 9-volt batteries, an improvised switch, and a hot wire initiator, and both devices were booby-trapped. When each package was opened, the spring tension applied to the switching mechanism released, completing the electrical circuit. Electrical power reached the improvised hot wire initiator, causing it to ignite the main charge explosive. Earlier UNABOM incidents investigated by the FBI are described, and sketches of some of the IED's are included. 6 figures