Kazan police said university teacher Igor Danilevsky, 38, was arrested and confessed to the double homicide.
The names of the victims were not released but police said Danilevsky was an acquaintance of the younger woman.
Investigators said the suspected assailant may have put the slogan calling for the release of jailed members of the rock group Pussy Riot on the wall to throw off police. Pussy Riot supporters speculated the killings and the reference to the group may have been an attempt to discredit the band, the Russian news agency RIA-Novosti said Friday.
Three members of the rock group were and convicted and jailed after entering a Moscow cathedral in March to perform a song critical of Russian President Vladimir Putin. Their trial divided Russians and sparked protests.