Mustard and Black have been friends since college. Mustard incubated Black’s company in its early stages, and the two grew to be successful entrepreneurs through their cooperation. Black invited Mustard to his ship to convince him to invest in a new business venture where Mustard told Black in confidence that he was planning on drilling for oil close to the islands.
Dr Black, the ruthless businessman he is, took that idea as his own and started preparing his own drill. On top of that, Dr Black also ended the friendship with Mustard, having only used him for his connections in the finance world. Perhaps Mustard's greed was enough to push him over the edge and end Dr Black's life?