My opinion is based on my experience and training as a law enforcement officer in the US.
I do not feel Diver #1 (instructor) would be criminaly liable, but most likely held civilally liable based on the scenario you described.
Your scenario described Diver #1's actions only as encouraging Diver #2 to dive again. This means Diver #2's choice to dive was conensual. Diver #1 did not do anything directly to cause the resulting death, therefore the intent was not there (knowingly, intentionally, or with criminal negligence). This would be different if he had an active part such as knowingly giving Diver #2 faulty equipment, intentionally shutting off Diver #2's tank, or some other similar action.
Civilally, I think Diver #1 would be working the rest of his life to repay the judgement awarded to Diver #2's family.
Just my .02
I do not feel Diver #1 (instructor) would be criminaly liable, but most likely held civilally liable based on the scenario you described.
Your scenario described Diver #1's actions only as encouraging Diver #2 to dive again. This means Diver #2's choice to dive was conensual. Diver #1 did not do anything directly to cause the resulting death, therefore the intent was not there (knowingly, intentionally, or with criminal negligence). This would be different if he had an active part such as knowingly giving Diver #2 faulty equipment, intentionally shutting off Diver #2's tank, or some other similar action.
Civilally, I think Diver #1 would be working the rest of his life to repay the judgement awarded to Diver #2's family.
Just my .02