From Wiki....
1886 - The Pimlico Mystery - Following the suspicious death of Thomas Edwin Bartlett, his wife Adelaide was charged with murder. It was found that Bartlett's stomach contained a fatal quantity of chloroform, although this had not caused any damage to his throat or windpipe. Adelaide Bartlett was later acquitted, possibly because the prosecution were unable to explain the death, or how she could have committed the crime.
1888 - Jack the Ripper - At least five prostitutes were murdered and mutilated by an unidentified serial killer, dubbed "Jack the Ripper" by the press. The murders eventually stopped and the murderer was never apprehended.
1910 - Dr. Crippen case - Hawley Harvey Crippen, an American-born doctor, used his position in a London pharmaceutical company to poison his wife before fleeing the country with his mistress. However, due in part to the newly developed wireless communication, Crippen was apprehended by Scotland Yard detectives onboard the SS Montrose shortly before its scheduled arrival in Quebec.
1911 - The Siege of Sidney Street - A shootout between unarmed London constables and a group of Latvian anarchists led by George Gardstein left three officers and Gardstein dead. British authorities then laid siege to the anarchists' safehouse on Sidney Street, meeting fierce resistance from the three anarchists inside. A fire broke out after a six-hour battle and, while the bodies of Fritz Svaars and William Sokolow were found, their leader Peter Piaktow was not located.
1915 - Brides in the Bath Murders - George Joseph Smith, a con artist and bigamist, murdered three of his wives before being arrested and executed on August 13, 1915.
If anyone would like to elaborate more on these crimes, post here