Timothy McVeigh would himself seem to dispute your calling him a Christian.

He himself said:

In his letter, McVeigh said he was an agnostic but that he would "improvise, adapt and overcome", if it turned out there was an afterlife. "If I'm going to hell," he wrote, "I'm gonna have a lot of company." His body is to be cremated and his ashes scattered in a secret location.

http://www.theguardian.com/world/200...1/mcveigh.usa4

So, I guess that would make him an Agnostic Terrorist.

I agree with your assessment that his bombing of the Oklahoma federal building was an act of terrorism by definition.