Peter Manuel: a further note

Further to the previous post on this blog, I have now obtained a copy of Wilson's book on Peter Manuel's trial. The following section is relevant:

'It is an appalling record for a man of thirty-one. But it is typical (except perhaps in degree) of the aggressive psychopath and there is little doubt that that is the appropriate label to hang on Manuel. It does not, however, explain matters. The causes of such a condition are as yet largely unknown and it is not yet possible to treat psychopaths, except the very young, with any real hope of success...
Before his trial, Manuel was examined by doctors, including eminent psychiatrists and neurologists, on behalf of the Crown and presumably found sane and fit to plead. The defence also had him examined, with a view to putting forward a special defence of insanity, but could not find support. They also considered putting forward a case of diminished responsibility, as explained to the jury by Lord Cameron, but were dissuaded from doing so by their client, who told them, with genuine laughter, that he "wanted nae mair o' that insanity business". It may be said that a plea of diminished responsibility, based on his being a psychopath, would not have availed him...'

(John Gray Wilson, The Trial of Peter Manuel: The Man Who Talked Too Much (1959) 230-231.)