Mary Ann Cotton had a number of names, Cotton being the name of her last husband. She killed her husband and her children for the insurance money. She was hanged in 1873 in Durham, 15 miles from my home. She was such a reviled figure that children in the late 19C had a skipping rhyme about her:
Mary Ann Cotton,
She's dead and she's rotten
She lies in her bed,
With her eyes wide open
Sing, sing, oh, what can I sing,
Mary Ann Cotton is tied up with string
Where, where? Up in the air
Sellin' black puddens a penny a pair.
Full info can be found here:
http://en.wikipedia.org/wiki/Mary_Ann_Cotton