8. Not A Jack But A Jill
In the mid-2000s, Australian scientist Ian Findlay managed to collect samples from the back of stamps used to send Ripper letters to the press.
Despite the large number of communications claiming to be from the killer, numbering in the hundreds, just a small handful — the "From Hell" letter, the "Dear Boss" letter, and the "Saucy Jack" postcard — are thought to be genuine writings of Jack the Ripper.
Findlay managed to collect samples from the letters, including the "Dear Boss" letter, which was said to be stained with the blood of one of the victims, Mary Kelly (a claim Findlay later disputed, saying the blood had a male profile). He then examined the samples using a process called Cell Track-ID, able to create a DNA fingerprint of sorts even with material over 150 years old.
Although the profiles were inconclusive, Findlay would state that it was possible Jack the Ripper could have been female. A Jill, then.
It's not just a modern spin, however. Sir Arthur Conan Doyle, the author behind Sherlock Holmes, suggested such a theory himself. After all, who but a woman — a midwife, perhaps — could walk the streets of London covered in blood, and not raise suspicion?
Other notable figures believed a female killer could be possible as well.