Kaczynski's letter bomb construction had several unique hallmarks that were used by the FBI in the construction of the profile of the "UNABOM" suspect -- in particular the inclusion of wood.elements such as handmade wooden boxes containing the bombs' component parts and wooden splinter shrapnel, including bark. The initial profile, however, was that of a "junkyard bomber" -- someone whose relatively-sophisticated mechanisms were accompanied by a payload of scavenged materials, suggesting not a formal education in engineering or an already-known domestic terrorist operation but a disgruntled blue-collar worker. Kaczynski had studied mathematics at an undergrad and graduate level, but not engineering; his interest in engineering grew out of his retreat to rural Montana in the late 1960s and early 1970s, after resigning from his teaching position at Berkeley. He appears to have studied texts related to self-sufficiency and pre-electrical technologies extensively during this time, what he called "wilderness skills", in a self-guided fashion -- this is also the period in which his social and political philosophy took shape, and it seems reasonable to me to believe that at this time he sought out materials related to bomb-making as well as carpentry.

In the most straightforward sense, Kaczynski was a self-taught bombmaker; he had a solitary disposition, did not know or like the contemporary activist groups who might have been willing to personally educate him on techniques of domestic terrorism, and did not have co-conspirators or collaborators. But in a more complex sense, his purpose was shaped by the milieu in which he lived during the 60s and 70s, the accessibility of both engineering-related materials suitable for self-education in bombmaking and perhaps materials explicitly outlining the creation of bombs intended for political uses. It's hard to identify just what Kaczynski used in the course of his self-education, both because he is reticent to share that information and because the FBI is fairly closed-mouthed about these specifics in the interest of not educating other bombmakers, but I think we have reason to believe Kaczynski was self-taught and to describe him that way.