Cornwell's book was released to much controversy, especially within the British art world, where Sickert's work is admired, and also among "Ripperologists", who dispute her research methods and conclusions.

Cornwell claims this marriage and the end of the friendship provided the spark which exacerbated his awareness of his disabilities and ignited a latent anger against the opposite sex.

She also points to Sickert's paintings and sketches, some of which show women in prostrate poses that Cornwell claims are similar to victims at their crime scenes.

Critics also note that Cornwell has said that she did not have a theory about the murders until about a year before her book was published and believed that the first suspect mentioned to her was the one who really committed the crimes.

In September 2014, Finnish molecular biologist Jari Louhelainen claimed that his DNA analysis pointed to a different suspect, Aaron Kosminski, which also provoked criticism and controversy.

The New York Times's December 2002 review by Caleb Carr was very critical, writing: Portrait of a Killer is a sloppy book, insulting to both its target and its audience.