It was Oliver Cromwell who murdered 3,000 Catholic men, women and children at the Massacre of Drogheda, when, after a siege, he put the entire population of the town to the sword.
For the principle of the thing, you know. To make an example: "Do not resist." Come to think of it, Cromwell had the same ethical notion as Alder Hey.
Not unlike Mary I did to the Protestants a century before. She even had Cramner burned at the stake even after he recanted.