Rumors have circulated that the incident was a terrorist plot .
The Russian Prosecutor 's Investigative Committee spokesman , Vladimir Markin , declared that the fire was caused by unsanctioned use of fireworks indoors .
Rumors have circulated that the incident was a terrorist plot , but the Russian Prosecutor 's Investigative Committee spokesman , Vladimir Markin , declared that the fire was caused by unsanctioned use of fireworks indoors .