The slogan appeared to have been written in the victims' blood, RIA Novosti reported.
Nikolai Polozov, a lawyer representing the three imprisoned feminist punk rockers, called the killings a "heinous dirty provocation."
"I regret that those monsters used the Pussy Riot name for such purposes," he said.
Investigators in the Republic of Tatarstan said the woman and her 38-year-old daughter were killed between Sunday and Tuesday -- both were stabbed several times. "Free Pussy Riot" was written in English on a wall over their bodies.
The members of Pussy Riot were convicted this month of staging a demonstration against Vladimir Putin before he was re-elected president at the Russian Orthodox Cathedral of Christ Our Savior in Moscow.
They were sentenced to two years each.