There very well could have been murder, but 100% rather than 60% fatalities might not have been remarkable..these were men from a famine-part of Ireland after a long sea voyage, probably emaciated to start with, immediately put to work apparently, malnourished, overworked, crowded into a little shanty, probably not enough blankets, protection from weather etc. The higher survival rate might have referred to a well-fed population with people caring for them. mg