A leading US-based human rights body has accused Russian security forces of torturing suspects after the attack on Nalchik in the North Caucasus.
The Nalchik attack left dozens of people dead
Human Rights Watch said torture had been used to coerce confessions.
Chechen-backed gunmen suffered heavy losses when they launched the attack on 13 October and sparked fighting in which at least 86 people were killed.
Prosecutors for the surrounding region of Kabardino-Balkaria have rejected accusations of police heavy-handedness.
HRW said its investigators had collected convincing evidence that at least eight people detained over the attacks had been subjected to ill-treatment.
Suspects were beaten and denied proper access to lawyers, it reported.
"The illegal practice of fighting one human rights abuse with another must be stopped immediately," HRW said.
Chechen PM injured
In another development, Chechen Prime Minister Sergei Abramov was seriously injured in a road crash in Moscow.
The head of Chechnya's Moscow-backed government was in a serious but stable condition after the crash - not said to be suspicious - on Thursday night.
He has been temporarily replaced by Deputy Prime Minister Ramzan Kadyrov, head of a militia often accused of human rights abuses in Chechnya.