The remains of four adults and six children were discovered by workmen during the £1.9 million restoration of Franklin's home at 36 Craven Street, close to Trafalgar Square. Researchers believe that there could be more bodies buried beneath the basement kitchens.
Initial estimates are that the bones are about 200 years old and were buried at the time Franklin was living in the house, which was his home from 1757 to 1762, and from 1764 to 1775. Most of the bones show signs of having been dissected, sawn or cut. One skull has been drilled with several holes. Paul Knapman, the Westminster Coroner, said, "I cannot totally discount the possibility of a crime. There is still a possibility that I may have to hold an inquest."
The principal suspect in the mystery is Doctor William Hewson, like Franklin a Fellow of the Royal Society, and the husband of Polly Stevenson, the daughter of Franklin's landlady, Mary Stevenson. Dr. William Hunter and Dr. Hewson ran a school of anatomy in Soho, but, after an argument, Dr. Hewson left to live in Franklin's house, where he is believed to have established a rival school and lecture theatre. Paul Knapman added: "It is most likely that these are anatomical specimens that Dr Hewson disposed of in his own house, but we are still not certain about the bones' exact age or origin."
You can read more in an older article at http://www.theforbiddenknowledge.com/hardtruth/ten_bodies.htm and later follow-up articles (that add very little new information) at http://io9.com/5901948/why-were-10-dead-bodies-found-in-benjamin-franklins-basement and at http://mentalfloss.com/article/30448/time-they-found-those-bodies-ben-franklins-basement.
My thanks to newsletter reader Anthony Stike for telling me about this mystery.