Navy prosecutors in Russia appealed the acquittal of two men blamed for the deaths of 20 people aboard the nuclear submarine Nerpa in a deadly 2008 accident.

The accident, in which a fire safety system was activated without permission, released poisonous freon gas, suffocating to death 20 men, including 17 civilian shipyard workers.

There were 208 people on board the vessel at the time conducting sea trials in the Sea of Japan.

Capt. Dmitry Lavrentyev was charged with abuse of authority in the accident, and engineer Dmitry Grobov was accused of causing death by negligence.

Lavrentyev and Grobov were acquitted of the charges April 26 on grounds the investigation into the accident had not been properly conducted. This was their second acquittal. A jury cleared the two men in September 2011, but the Supreme Court’s military board overturned the verdict in May 2012.

The Pacific Fleet navy prosecutors said Wednesday they think Lavrentyev and Grobov should be tried again, RIA Novosti reported.

 “In our opinion, Lavrentyev and Grobov are the only ones guilty of the accident. They are the ones who should be held responsible. We regret that the jury failed to understand this,” a spokesman said.

Other men on board the Nerpa at the time of the accident have written an open letter defending the actions of Lavrentyev and Grobov and instead blamed the defense industry for creating a fire-suppression system contaminated with a poisonous chemical, RIA Novosti reported.