The tragedy occurred late on November 8 while the Nerpa was undergoing sea trials in the Sea of Japan. Three submariners and 17 shipyard workers died in the accident. There were 208 people, 81 of them submariners, on board the vessel at the time.
"The suspect's psychological examination is prescribed by law," the spokesman said. "I cannot say how long it will take or where it will take place."
He added that a technical examination of the submarine and its systems would last at least a month.
Submariner Dmitry Grobov could face up to seven years in prison if found guilty of triggering the fire suppression system without permission.
Ensign Yevgeny Ovsyannikov, a technical specialist on the Nerpa, told Komsomolskaya Pravda that the tragedy could have been caused by a computer glitch, not a crew member.
"We submariners are unanimous: a computer program failed. Previously, the submarine fire suppression system had always started manually on the commander's orders. Now it is launched electronically," Ovsyannikov was quoted as saying in Wednesday's edition of the popular daily.
He added that it was the first time the computerized system had been used on the submarine during the sea trials and that the computer had malfunctioned during tests while docked.
An expert who requested anonymity suggested that a toxic form of Freon could have been used in the fire suppression system.
The incident is the Russian Navy's worst since the sinking of the Kursk nuclear submarine in 2000, taking the lives of all 118 on board.