Photo of victim found on phone of teen accused of beheading teacher near Paris

Eleven people are still in custody in France following the beheading of a teacher Friday in a suspected Islamist attack.  CBS News correspondent Elaine Cobbe reports that counter-terror investigators are building a profile of the 18-year-old Chechen man who carried out the brutal attack on 47-year-old teacher Samuel Pety who police officials said had discussed caricatures of Islam's Prophet Muhammad with his class. 

Anti-terrorism prosecutor Jean-Francois Ricard said a text claiming responsibility and a photograph of the victim were found on the attacker's phone. He also confirmed that a Twitter account under the name Abdoulakh A belonged to the suspect. It posted a photo of the decapitated head minutes after the attack along with the message "I have executed one of the dogs from hell who dared to put Muhammad down."

Ricard said the attacker had been granted 10-year residency in France as a refugee in March, was armed with a knife and an airsoft gun, which fires plastic pellets. His half-sister joined ISIS in Syria in 2014, Ricard said. He didn't give her name, and it wasn't clear where she is now.

France's interior minister said Monday that police operations are underway into dozens of people who allegedly issued messages of support for the attacker after the beheading of a history teacher near Paris.

Gerald Darmanin said on French radio Europe 1 that at least 80 cases of hate speech have been reported since Friday's attack.

Paty was beheaded in Conflans-Sainte-Honorine, northwest of Paris, by a 18-year-old Moscow-born Chechen refugee, who was later shot dead by police. 

French President Emmanuel Macron held a defense council on Sunday at the Elysee presidential palace. The government will reinforce security at schools when classes resume on Nov. 2 after two weeks of holidays, Macron's office said.

A national homage is to be held for Paty on Wednesday.

Tens of thousands of demonstrators gathered on Sunday across France in support of freedom of speech and in memory of the slain 47-year-old teacher. Many chanted "je suis prof" – I am a teacher – echoing the chants of Je suis Charlie after the Charlie Hebdo attack in 2015, Cobbe reports.

French authorities said they detained 11 people following the killing. Darmanin said they include the father of a student and an Islamist activist who both "obviously launched a fatwa," or religious ruling, against the teacher.

A man who said he was the father of a student had posted a video on social media asserting that Paty had shown an image of a naked man and told students it was "the prophet of the Muslims." He called on other angry parents to contact him, and relay the message.

Darmanin said authorities were also looking into about 50 associations suspected of encouraging hate speech. Some will be dissolved, he said.

The president of the Conference of imams in France, Hassen Chalghoumi, said "we are hurt, we are condemning this barbaric act," on French news broadcaster BFM TV. "Samuel is a martyr of freedom."

"Barbarism has no place in schools nor elsewhere in France," he said.

Chalghoumi, who is an imam in Drancy, a suburb northeast of Paris, said he had received death threats and insults on social media from radical Islamists in recent days.

Justice authorities opened an investigation for murder with a suspected terrorist motive. At least four of those detained are family members of the attacker, who had been granted 10-year residency in France as a refugee in March. He was armed with a knife and an airsoft gun, which fires plastic pellets.