A sailor has confessed to causing the deaths of 20 people on a Russian nuclear submarine – but there are some who think investigators have got the wrong man.

The man suspected of causing the death of 20 people on board the Nerpa has gone through everything he did at the time of the disaster with investigators. The Navy's main suspect confessed that it was he who turned on the sub's fire extinguishing system, releasing the poisonous Freon gas.

The crew and civilians on board did not have time to put on breathing masks before the oxygen supply ran out.

“The suspect has admitted his guilt. Investigators continue to work with him. The investigation has been launched under article 352 of the Criminal Code – violation of navigation rules. Investigators are working to determine the degree of responsibility of various officials, both military and civilian in the tragedy that resulted in casualties,” said Vladimir Markin, a member of the Investigation Committee of the Russian Prosecutor’s Office.

Experienced sailors say there are several reasons why the seaman under investigation may have caused the incident, from bad orders to plain carelessness.

“This may have happened because he was given a wrong command, or he may possibly have activated an incorrect system. The sailor must have been tired, and then we have the human error factor,” said retired captain, Aleksandr Milanov.

However, doubts have surfaced whether the crew member taking the blame is the real culprit. Russia's Interfax news agency quotes another member of Nerpa's crew, who says he has known the suspect for a long time and that for him to make such a mistake would be completely out of character.

Meanwhile, RIA-Novosty news agency quotes sources in the investigative committee which suggest the investigation is also focusing on how this particular crew member gained access to a system he was not authorised to operate.

Thursday, November 13 was officially declared a day of mourning in Khabarovsk Region. Twelve of the victims were buried at a local cemetery in Komsomolsk-on-Amur as honorary citizens of the town.

A memorial will be built to remember all those who died.

The accident took place in the Pacific Ocean on November 8, while the vessel was undergoing trials.

The 20 who perished -17 from the shipyard delivery team and three sailors – were killed by the release of Freon, a poisonous gas used to put out fires, which was triggered when the fire extinguishing system was accidentally turned on. Twenty-one others were injured.

The main findings of the official investigation will be announced on Friday, November 14.