The Black Hole of Calcutta

From 1600 the English East India Company traded with the Indian sub-continent, tried to avoid becoming involved in internal politics, and made fortunes for its principal employees. But one event was crucial in converting English influential opinion to an interventionist policy - the infamous Black Hole of Calcutta, when, on the night of June 21, 1756, 123 English prisoners suffocated to death on the orders of Siraj-ud-Daula, Nawab (ruler) of Bengal. Thenceforth England regarded Indian rulers as savages, and considered that they were unfit to govern India. From this it was but a short step to the establishment of complete English political control over the areas in which the English Company traded. But what is the truth of the Black Hole? Did 123 died? Did Siraj-ud-Daula deliberately order their deaths or, indeed, did the Black Hole happen at all?