A criminal case was launched into the deaths of two divers who drowned during dam maintenance in Russia’s northern Republic of Komi, a spokeswoman for the regional investigation department said on Tuesday.

The deaths occurred on Monday morning. When one diver failed to surface at a scheduled time, the other dived down to rescue him. It is unclear why both divers drowned.

“The bodies of both divers have been recovered by rescuers and sent to a coroner,” spokeswoman Svetlana Korovchenko said.

Charges of safety violations carry a maximum punishment of up to seven years in prison if human error or mismanagement is proven to have contributed to their deaths.