E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
One who snatches or purloins bodies, newly buried, to sell them to surgeons for dissection. By a play on the words, a bum-bailiff was so called, because his duty was to snatch or capture the body of a delinquent.
The first instance of body-snatching on record was in 1777. It was the body of Mrs. Jane Sainsbury from the burial ground near Grays Inn Lane. The men, being convicted, were imprisoned for six months.