I think its the difference between depression and depressiveness.

Depression is a mental state that can be masked. Depressiveness is a behavior pattern that telegraphs the mental state of depression.

So someone can technically be a schizophrenic but is not in such distress that anyone observing them would know at a glance and therefore think them a 'nutcase'. Its like someone who is homeless but clean and well dressed. At first glance, you don't think of them as living in the streets.

I have no idea whatsoever if the intruder actually had any sort of mental illness. He simply may have had values that we feel makes him a bad person, but that does not mean he is a "sick" person. He may enjoy killing. Well, alot of hunters enjoy killing. He may prefer adult, consenting females, but perhaps lacks the social skills to obtain them. Is he 'sick' or is he simply posessed of a separate set of fundamental values than most people have. One prospective juror when being questioned in a sexual abuse case actually expressed the viewpoint that it was acceptable for a man to make use of a daughter if his wife was for some medical reason unable to have sex. The young prosecutor was visibly shaken by his views despite the courtroom setting. She obviously got rid of that prospective juror but quick. However, it was her reaction that was significant. Its not a set of values that she shares or even felt would ever be expressed in speaking to a potential juror.