Do you think you can live all your life with a totally normal person showing no symptoms of psychological or psychiatric illness or even a symptom of personality disorder to wake up one day in front of a criminal?!
And that even an expert in psychology can remain himself deceived since neither the tests, nor the speeches nor even the missed acts, nor the unsaid, nor the body language could have revealed the reality and that the unconscious has not never revealed itself by a tiny thing!
Is it true that you can sleep with your enemy all your life only to wake up victim of a criminal act?
Is there this pessimistic probability?
Or is there something missing in our attention?
And if we have been vigilant then can we always this unfortunate destiny?
What happens a few minutes before the action?
This is a fascinating question 😯
I would say yes mainly because this has happened many times before with the sudden onset of a neurological illness. We may consider for example Capgras' delusion which can lead to violence.
However, if we restrict ourselves to non-neurological disease such as a tumour causing aggression or perhaps a pheochromocytoma or adrenaline secreting tumour this becomes tougher to answer.
I think those nearest to us are often the hardest to view objectively, so even if you're a trained psychologist you can be blind to the development of dark traits.
I believe that there are hints, but these can be especially subtle and almost impossible to pick up on. The only case as I suggested where there may be little to no warning would be the case of an acute onset of a neurological disorder.
I'm a bit of an optimist so I like to believe that if we educate ourselves enough and apply careful observation then we can detect certain signs arising.