If proof were needed that Amazon needs to introduce a zero star rating, this, folks, is it. This book is utterly uninformed, badly constructed and littered with declarations of personal (often unsupported) belief, rather than with facts.
The prime arguments it contains are all patently incorrect: Sickert had an operation on his penis - not true. The operation (actually to his anus) traumatised him - not true. It instilled in him a hatred of women, a result of a botched operation that left him impotent - not true. His works show hints of violence towards women and clues to his crimes - subjective, but almost certainly not true. He wrote (at least some of) the Ripper letters - widely discredited, especially by Sickert experts. His DNA matches that found on some Ripper letters - not true (Sickert was cremated and no DNA traces remain; even if the vague results drawn of 110-year-old letters and paintings constitute evidence, they suggest similar biological traces, which 1 to 10 percent of the population shares.... He killed again well after 1888 - so totally unfounded it beggars belief. He could well have been in Whitechapel at the time - in fact, he spent most of the period in Northern France. I could go on... but I think we're starting to get the idea. It's all so incredibly inept.
Walter Sickert, from all the sources left behind of his life and friendships, was not a violent or especially angry man. He was selfish and admittedly a little weird, but that does not a Ripper suspect make. In total, Cornwell's impression of a psychotic villain who managed to conceal his homicidal tendencies until his death in 1942 to every one of his friends, relatives, artistic acquaintances etc. totally fails to convince.
This is not history. It's not even a proper conspiracy theory. It's just total tat.