Police Superintendent Thomas Arnold (7 April 1835 – 1907) was a British policeman of the Victorian era best known for his involvement in the hunt for Jack the Ripper in 1888. It was his opinion that Mary Jane Kelly was not a victim of the Ripper.
The son of Thomas and Elizabeth Arnold, Arnold was born at Weald in Essex and joined the Metropolitan Police's B Division (Chelsea) on 19 March 1855 and resigned on 20 September 1855 to fight in the Crimean War. At the end of hostilities he rejoined the Police on 29 September 1856, being attached to K Division (West Ham) with the warrant number 35059. He served most of his career in London's East End. He was promoted to Inspector on 14 March 1866, and was transferred to B Division.
In 1887 Arnold was involved in the Lipski Case, and by 1888 he was Police Superintendent of H Division (Whitechapel) at the time of the Whitechapel murders in that district. After the "double event" of the early morning of 30 September 1888, police searched the areas near Mitre Square and Berner Street in an effort to locate a suspect, witnesses or evidence to the murders of Elizabeth Stride and Catherine Eddowes. At about 3:00 a.m., Constable Alfred Long discovered a bloodstained piece of cloth near a tenement building on Goulston Street. The cloth was later confirmed as having been cut from Eddowes' apron.