The fire broke out at the psychiatric clinic early Friday, killing 38 of the 41 people believed to have been inside, RIA Novosti reported.
Police said most of the victims died in their sleep of smoke inhalation and likely were sedated by prescribed medicine.
On Saturday, Moscow and surrounding areas held a day of mourning for the incident.
"All scheduled entertainment events have been canceled in connection with the mourning," the press service for acting Moscow Region Gov. Andrei Vorobyov said.