A quasi-opposition party led by Sergei Mironov, A Just Russia, initiated the investigation, saying about 6,000 "dead souls" voted in the Dec. 4 election, a regional investigations committee spokesman told RIA Novosti.
Two makeshift polling stations were allegedly set up in the city's Kommunar residential district, though both remained closed until the afternoon and elections monitors were prevented from entering.
The local electoral commission reported 6,000 votes from the polling stations, allegedly from local students who were told to hand in their passports on election day.
Most of the voting documents were destroyed Jan. 7 in a purportedly accidental fire at a local administration building, the news agency said.
Tens of thousands of people rallied in December across Russia to protest alleged vote fraud favoring the pro-Kremlin United Russia party.