Final answer:
The notorious unsolved crime spree in East London is attributed to Jack the Ripper, who killed at least five women in the 1880s, and whose identity still remains unknown.
Step-by-step explanation:
The most notorious unsolved crime spree referred to in the question is attributed to the serial killer known as Jack the Ripper. Jack the Ripper is believed to have killed at least five women in the East End of London during the late 1880s. The identity of this killer remains unknown to this day, making the case one of the most infamous in the annals of criminal history. These murders, often referred to as the Whitechapel murders, caused a panic and media frenzy at the time due to the gruesomeness of the murders and the brazenness with which they were committed. Despite extensive historical research and numerous theories, the true identity of Jack the Ripper continues to elude experts and remains a topic of fascination in popular culture.