There had been murderers before, and then there was Jack. Except, of course, there was no Jack the Ripper. There were murders—ripped prostitutes attested to that—but the business name was probably a journalist’s invention. The name caught on and inspired red-ink-imbibing, red-pillar-box-filling writers (many of them women) who sent out hundreds of police-troubling letters composed of ravings and penny-dreadful nightmares. Jack has inspired social reformers, criminologists, get-rich-quick writers and publishers, film-makers, fanatics and seekers of truth. Yet this franchise for murder may be based on simple, clumsy, violent crimes committed by an ordinary, banal man who could have been arrested…