Yeah, as I understand it the Unabomber was politically motivated terrorism. He also had the distinction of being a pretty smart guy, which is unusual for the demographic that gets into mass murder.
I actually thought it was fairly common for mass killers (other than those whose mass killing is confined to a single mass casualty attack / killing spree), if for no other reason than not being smart makes it more likely that you get caught before your killing reaches the level of "mass".
I wouldn't say it's "unusual" [2]
[0] http://maamodt.asp.radford.edu/Psyc%20405/serial%20killers/B...
[1] https://en.wikipedia.org/wiki/Andrew_Cunanan#Early_life
[2] http://www.examiner.com/article/22-serial-killers-with-high-...