No, the opposite is almost always the case: they always have some type of rationalisation.
My guess is that you're using rationalisation in lieu of something like reasonable justification.
Also calling it mental illness is a massive cop-out indeed. It bypasses the blame to a hypothetical unnamed illness. It also creates/fuels the false perception that mentally ill people are dangerous or criminals when in fact they are more likely to be victims of crimes. I never understand why people would make excuses for terrorists!
I am saying no rationalizing from our point of view not theirs.
And you can call it something else, but for me commiting these acts are insane.
Of course they need to be punished to the full extent of the law