The lawyer said Sergei Alekseichuk should receive 25 years at a maximum-security prison colony for orchestrating the 2004 apartment explosion, which killed 58 people and injured 170 more.
Alekseichuk, a former employee of the city gas service, is accused of intentionally opening gas valves in the nine-story apartment block that led to a massive explosion. He faces murder and terrorism charges.
Alekseichuk has pleaded guilty to the charges, but his lawyers say he did not intend to kill the building's residents when he opened the valves.
The final verdict is due to be delivered on 13 December.