Of course he was a liar; but why lie about what motivated him? Dobson could do nothing to save Bundy, and Bundy knew it. You either haven't read/seen the actual interview or at least don't remember it, because his description of how violent pornography motivated him rang true.
Not only do I remember the interview, I remember it very well. One of the dead give-a-ways in the interview is Bundy's repeated pretenses of remorse, regret, and guilt. Bundy was a sociopath, he felt none of those things he portrayed to Dobson. He was incapable for feeling those things. He was however clever enough to present the facade of the remorseful killer, who can't even talk about the murder of a 12 year old girl, because it's just too painful for him to talk about. Give me a break. He was feeding Dobson a steady diet throughout the entire interview.