experts have long warned the sub was not certified to dive so deep. in 2018, the chairman of a committee of 38 concerned submersible experts wrote to ceo rush asking him to adhere to our industry accepted safety guidelines and protocols for ultimate success. in 2021, discovery channel host josh gates decided against taking the sub down to the titanic for his tv show. i just felt as though the sub needed more time and needed more testing, frankly. reporter: investigators don t yet know why the sub imploded. it might have surrendered to the crushing pressure nearly 400 times what it is at sea level. perhaps a fatigue crack developed in the titanium carbon fiber shell after so many deep dives. it s hard to imagine, it s one empire state building made of lead sitting on top of you at that level. reporter: in a hauntingly cruel twist of fate, stockton rush s wife wendy lost relatives in the