Punish only when the behaviour is modifiable.

I am playing a tennis match, we see a man walk by
there is obviously something wrong with his motor actions
for his arms fly up as is he walks as if some puppet master.
During the change over between games we watch him
receded still flailing his arms.
My playing partner tells me a story. 'Got to tell you a
story about the guy. You know Alan (another player we know
and an inveterate do gooder) ...well we are playing once
and he sees him and talks to him and invites him for a coffee.
Well while they are sitting down the guys arm flies up
catches him under the chin, and breaks a crown in his mouth
whihc has just cost him hundreds at the dentist. He takes
advices and decides this poor chaps caters for damages.
But he loses because the Judge rules that the defendant
could only be found guilty if his behaviour, the flailing
are, was modifiable.
'So what happens if someone actually murders another
while they are sleep walking?'
'The same thing, they are only guilty if their behaviour
is modifiable.'