The 40-tonne submarine that the inventor had built in ... inventor had changed his story and told them she died on board of carbon monoxide poisoning while he was up on deck.

Submarines are built to be difficult to find ... With a possible shortage of oxygen and a build-up of carbon monoxide, suffocation is the number one risk. Oxygen can be supplied either through ...

The submarine was driven deeper, to a dangerous 525 feet — 200 feet beyond its recommended depth. As oxygen levels dwindled ...