Relatives of a Navy SEAL hopeful who drowned last year in a Staten Island pool have filed a lawsuit against the city of New York.

The young man, Bohdan Vitenko, 21, was found face down in the water along with a friend, Jonathan Proce, also 21. Proce worked as a lifeguard at another pool and both were training for elite military units, according to reports.

The incident happened at Lyons Pool and Vitenko was pronounced dead at the scene. Proce died in a hospital a few days later.

Based on witness accounts that indicted the men were practicing underwater breath-holding exercises, experts and family members believe that they died as a result of what’s known as shallow water blackout.

The New York Post notes that Vitenko’s family claims the lifeguards should have noticed the men doing the exercises and stopped them.