The Metropolitan Police only have four viable suspects in the Jack The Ripper case. The four suspects have been 'nominated by contemporary police officers'.
• Aaron Kosminski, a poor Polish Jewish resident in Whitechapel;
• Montague John Druitt, a 31 year old barrister and school teacher who committed suicide in December 1888;
• Michael Ostrog, a Russian-born multi-pseudonymous thief and confidence trickster, believed to be 55 years old in 1888, and detained in asylums on several occasions;
• Dr Francis J. Tumblety, 56 Years old, an American 'quack' doctor, who was arrested in November 1888 for offences of gross indecency, and fled the country later the same month, having obtained bail at a very high price.
Sir Melville Macnaghten nominated the first three suspects, Aaron Kosminski, Montague John Druitt and Michael Ostrog. Macnaghten joined the Metropolitan Police as an Assistant Chief Constable in 1889 he was second in command of C.I.D. (Criminal Investigation Department) at Scotland Yard. Macnaghten's three suspects were detailed in a report dated 23rd February 1894. It is important to note that there is no evidence of contemporary police suspicion at the time of the murders in 1888 - just subsequent reports. Sir Melville Macnaghten's report is said to contain "several odd factual errors". Macnaghten's favourite suspect is believed to be Montague John Druitt.
The head of C.I.D., Dr Robert Anderson, together with Chief Inspector Donald Swanson believed that Aaron Kosminski was the murderer.
Dr Francis J. Tumblety was "amongst the suspects" during the time of the murders. Tumblety was "to my mind a very likely one" according to the former head of Special Branch, ex-Detective Chief Inspector John George Littlechild. Littlechild held this position at the time of the murders in 1888. Chief Inspector Littlechild had made his thoughts official in a letter dated 23rd September, 1913 addressed to criminological journalist and author George R Sims.
There is no hard evidence against any of these suspects.