. >> brian levin is a criminologist who specializes in analyzing acts of so-called lone-wolf violencewas influenced by the anti-tax movement. >> he was the prototypical lone wolf. the more they go off alone, the more that anger festers and they're able to get caught in a web of a belief system, which when coupled with this emotional instability becomes a volatile and dangerous mix. and it is most likely to be directed against a symbolic target that they believe is at the root of their setbacks and pain. and this is -- this is payback. it is not just political. it is personal. >> joe stack would remain in california in the late 1990s where he continued to run afoul of the irs. he formed two software companies and records show he failed to file corporate taxes on either. he began to funnel his anger and frustration, targeting the irs. >> this was not someone who was just going to go and hurt somebody randomly or just go after any government official. this was someone who wanted to declare war on the irs and to have a movement continue after he was gone to do it as well. >> coming up, jo