Some relatives don't believe the official death toll of 64 and have produced a list of 85 people missing.
In the Siberian city of Kemerovo the first funerals have been held for some of the 64 people known to have died in Sunday's shopping mall fire.
Forty one children are known to have perished.
Wednesday was a day of national mourning and elsewhere in Russia - candles were lit and flowers laid at rallies in several cities, including St Petersburg and Moscow.
Corruption and lax fire safety standards at the Winter Cherry shopping mall may have been to blame and both relatives and locals are enraged at the response to the tragedy.
Relatives say they have compiled a list of 85 people, most of them children, who are still missing - many of them don't believe the official death toll.
Investigators said fire exits had been illegally blocked, the public address system had not been switched on, the alarm system was broken, and the children had been locked inside cinemas.
President Vladimir Putin has promised the relatives that those responsible for what he called criminal negligence would be punished.
The fire swept through the upper floors of the shopping centre, where a cinema complex and children's play area were located, on Sunday afternoon.
Alexander Bastrykin, head of Russia's Investigative Committee, which handles major crimes, told Putin the fire alarm system in the mall had been out of order since March 19, and that a security guard had not turned on the public address system to warn people to evacuate the building.
He said five people had already been detained.