Police in Kazan found 'Free Pussy Riot' written on the wall of a double murder crime scene Reuters

The bodies of two women have been found beneath a message calling for the release of jailed members of the punk band Pussy Riot, Russian investigators have said.

The deaths have prompted anger among Kremlin supporters, who have warned that the musicians were encouraging dangerous radicalism. But supporters of the band, three of whose members were given prison sentences earlier this month, immediately cast doubt on claims that the murders were the work of a Pussy Riot fan.

One Russian investigator cautioned that the killer was possibly trying to mislead police by drawing attention to supporters of the punk provocateurs.

Investigators said the two victims – a 76-year-old and a 38-year-old woman – were killed in the city of Kazan at the weekend.

"The words 'Free Pussy Riot', presumably written in blood, were found at the scene of the crime, on the walls of the flat," the federal investigative committee said on Wednesday night.

The tabloid Life News, known for its sources within the Russian police and security services, published images of the graffiti, showing the words "Free! Pussy Riot" written in English on flowered wallpaper. The tabloid's owner, Ashot Gabrelyanov, tweeted: "If you still think that breaking the norms of behaviour in a church doesn't change anything, then I recommend you read the latest news."

Three members of the feminist punk collective – Maria Alyokhina, Nadezhda Tolokonnikova and Yekaterina Samutsevich – were sentenced to two years in prison this month on charges of "hooliganism motivated by religious hatred" after a performance criticising President Vladimir Putin in Moscow's main cathedral. Emotions over the trial – and the role of the Russian Orthodox church – remain heated.

Opposition activists immediately said the alleged graffiti were an attempt to smear the band and their supporters. Several noted that a statement from local investigators in Kazan, the capital of the mainly Muslim republic of Tatarstan, made no mention of the words. Local news reports also made no mention.

"This is an attempt to strike at all supporters of the group," Pyotr Verzilov, Tolokonnikova's husband, told the news site Gazeta.ru.

Nikolai Polozov, a lawyer for the band, tweeted: "What happened in Kazan is horrible. Pussy Riot was always for nonviolent protest. This incident is either a horrendous provocation or [the work of] a psychopath."

The Pussy Riot trio were sentenced on 17 August following a heated trial. Members of the band said the case against them was the opening shot in a new campaign of repression against political activists and freedom of expression.

In the wake of the verdict, wooden crosses outside Orthodox churches throughout Russia, and in the Ukrainian capital, Kiev, have been knocked over, prompting further anger among Russia's religious community against the band and their supporters.

The case has invigorated the anti-Kremlin opposition, which has vowed to turn out in the tens of thousands for a demonstration on 15 September.