Black Museum

"Mr Lusk, Sir I send you half the Kidney I took from one women preserved it for you tother piece I fried and ate it was very nice. I may send you the bloody knife that took it out if you only wate a whil longer signed Catch me when you can Mishter Lusk" -"From Hell" letter attributed to Jack the Ripper

Originally started by one of Scotland Yard's Inspectors for teaching purposes, what was once a smattering of criminal odds and ends confiscated from prisoners had expanded into a museum-worthy collection within a year. Coined the 'Black Museum' in 1877 but more commonly called 'Crime Museum', the intriguing displays cover every sort of criminal activity you can think of, with categories everywhere from Notorious Poisoners to Murder of Police Officers.

So what is housed in this private museum in room 101 at New Scotland Yard? Tools of the killing trade on both sides of the fence, including murder weapons and previously used nooses and death masks.  Artifacts that would make any true crime fan squirm; the fake De Beers diamond, the stove that serial killer Dennis Nilsen used to dispose of what was left of his victims, the umbrella that fired the ricin-filled pellet that was used to assassinate Bulgarian dissident Georgi Markov, and perhaps the most chilling display, the infamous "From Hell" letter supposedly written by Jack the Ripper.

The full collection has over 500 items related to 20th-century crimes, and still serves as a training tool for police officers from all over the country, who are currently the only people allowed to visit the museum. Even with a badge to gain entry, the museum's popularity makes it difficult for law enforcement officers to get an appointment. The collection is not currently open to the public, but discussions on changing that are in progress. 

Update as of April 2021:  Scotland Yard has moved its headquarters to new premises at Westminster embankment, and the Crime Museum is housed within it. It is now solely a training museum for police officers and is not open to the public. Some exhibits are at the British Museum.