They chose to focus on the hangman, bumbling Robert 'Nosey Bob' Howard who also hanged the Aboriginal tracker, Jimmy Governor (later made famous in Thomas Keneally's The Chant of Jimmy Blacksmith) and so many others.
He was called Nosey for the simple reason that he didn't have one. He was born with a nose but a horse kicked it off, leaving him with just two holes in the centre of his head through which to breathe. Given the ghastly nature of his face, being the hangman was the only job he could get.
Nosey Bob executed so many people, you'd think he'd have gotten good at it - but no.
He was utterly hopeless, and Louisa died a terrible death at his hands.