 It is not clear just why MI6 would recruit a man who was known to be planning to defect to the Soviet Union to spy against the Soviet Union or why Crabb would agree to such a mission if he really had decided that he wanted to live in the Soviet Union.The British diving expert Rob Hoole wrote in 2007 that Crabb had probably died of oxygen poisoning or perhaps carbon dioxide poisoning, and that Crabb's age and poor health caused by his heavy drinking and smoking had made him unsuitable for the mission that he had been assigned.In support of the death by misadventure theory, Hoole noted that before disappearing on his second attempt to dive "Ordzhonikidze", Crabb had during his first attempt experienced equipment failure, which suggested that Crabb's equipment was not up to standard.