Well, all I can say is God Help You! if you take all of your *wisdom* from the Great God Science and people with Higher Ed Degrees
A lot of scientists are truly brilliant; but a lot also have supreme book-learning while possessing very little good sense.
As you admit, a blood test cannot determine emotional or mental derangement. But what used to be considered ‘normal’ people of ‘average’ intelligence could reliably sense when something was ‘not right’.
If it goes to trial, a jury of ‘normal people’ will decide if what happened was ‘criminal’ - not you nor I.
I just don’t have a problem with the arrest, or with having the case investigated. A man of diminished capacity died who WOULDN’T have died, if someone hadn’t played around with him just for laughs.
But in a worldly court of law neither you,nor I,nor anyone else can be certain of what did,and did not,happen on that day.
So...not guilty in a court of law (reasonable doubt) but *very* possibly guilty in The Final Court.