There’s no credible motive but in 1903 that doesn’t matter, the prosecuting barrister can always blind the jury with a little bit of brain:
Like you, members of the jury, I have at different moments of the trial, convinced as I am and as you will be of the prisoner’s guilt, I have found myself asking, but why, but why? And this is what I would say to that question. It really does seem to point to a person who did these outrages from some diabolical cunning in the corner of his brain.
From Arthur and George by Julian Barnes. Jonathan Cape: London, 2005.
Mind Hacks 