Now, I've not read it myself, but the good folk at the NYT Book Review have tipped me off that Truman Capote's In Cold Blood set the stanadrd for narrative non-fiction works based around a single incident which is used to explore bigger ideas about the time in which it occurred.
Summerscale does seem to sense the need to pan out beyond the crime scene into the realities of Victorian life and the sub-plots which spin off towards the turn of the century and on the whole I think, achieves this successfully.
Yet the author admits in the afterward that in writing this book, she herself almost lost sight of the victim. I think the problem she had to grapple with is not unlike the central difficulty at the scene itself, which for a while unhinged the career of Jack Whicher himself — the limitations of Victorian-era CSI meant not only that there wasn't quite enough evidence to get a successful conviction first time round, but also that there isn't quite enough detail in the core crime story to drive the narrative from cover to cover, and just occasionally one really can feel the padding being applied.
Still I can wholeheartedly recommend this book, even though I know Richard and Judy have already done the honours!