When did Mary start killing Protestants?

Mary Tudor, Mary I was queen of England and Ireland from 1553 to 1558, was the daughter of Henry VIII and Catherine of Aragon. She was widely known for the executions of Protestants, which gained her the nickname of 'Bloody Mary'. One of her first actions after her ascension to the throne was to release several Roman catholic lords that were imprisoned, she had never agreed with England's break up with Roman Church, she tried to reconcile with the Pope Julius III, and, as part of this process, she started a series of executions of rich and important Protestants that started in the year 1555.