Originally Posted by Bridewell
It's difficult to determine the thought processes of such an essentially irrational individual.
Yes, and no. We might not understand what is fun about killing somebody, but we can understand why the midway at the state fair isn't as fun once you've been to Disney World. Also, why you don't want to eat a big meal an hour after you've just had one, but if you get interrupted three bites into dinner, you might feel hungrier than if you'd never sat down at all. That's latter one is why no one is ever surprised by the idea that after being interrupted during the Stride murder, JTR didn't get spooked and go home, but rather went immediately in search of another victim, and mutilated her to a greater degree than he had done so far.
Even people with pathologies still operate with general consistencies. And I would call JTR pathological, not really irrational. Irrational is like trying to play chess against a computer programmed to play backgammon. JTR continued to act in his self-interest, by avoiding the police, and seems to have cased the areas a bit before he committed any specific crime-- knowing the timing of a policeman's beat, for example. None of that is irrational.