After the IS affiliate claimed responsibility, U.S. intelligence backed up their claims. French President Emmanuel Macron said France has intelligence pointing to “an IS entity” as responsible for the Moscow attack.

As Putin spoke, calls mounted in Russia to harshly punish those behind the attack.

Russia’s Prime Minister Mikhail Mishustin said the investigation is still ongoing but vowed that “the perpetrators will be punished, they do not deserve mercy.”

Former President Dmitry Medvedev, now deputy head of Russia’s Security Council, urged authorities to “kill them all.”

The attack Friday night on Crocus City Hall on the western outskirts of Moscow left 137 people dead and over 180 injured, proving to be the deadliest in Russia in years. A total of 97 people remained hospitalized, officials said.

As they mowed down concertgoers with gunfire, the attackers set fire to the vast concert hall, and the resulting blaze caused the roof to collapse.

The search operation will continue until at least Tuesday afternoon, officials said. A Russian Orthodox priest conducted a service at the site Monday, blessing a makeshift memorial with incense.

The four suspects were identified in the Russian media as Tajik nationals. At least two of the suspects admitted culpability, court officials said, although their conditions raised questions about whether their statements were coerced.

The men were identified as Dalerdzhon Mirzoyev, 32; Saidakrami Rachabalizoda, 30; Shamsidin Fariduni, 25; and Mukhammadsobir Faizov, 19. The charges carry a maximum sentence of life imprisonment.

Russia’s Federal Security Service said seven other suspects have been detained. Three of them appeared in court Monday, with no signs of injuries, and they were placed in pre-trial detention on terrorism charges. The fate of others remained unclear.

Russian media had reported the four were tortured during interrogation. Mirzoyev, Rachabalizoda and Fariduni showed signs of heavy bruising, including swollen faces. Mirzoyev had a plastic bag still hanging over his neck; Rachabalizoda had a heavily bandaged ear. Russian media reported Saturday that one suspect had his ear cut off during interrogation. The Associated Press couldn’t verify the report or videos purporting to show this.

Faizov, wearing a hospital gown, appeared in court in a wheelchair, accompanied by medical personnel, and sat with his eyes closed throughout. He appeared to have multiple cuts.

Peskov refused to comment on the suspects’ treatment.

Medvedev, Russia’s president in 2008-12, had especially harsh comments about them.

“They have been caught. Kudos to all who were chasing them. Should they be killed? They should. And it will happen,” he wrote on his Telegram page. “But it is more important to kill everyone involved. Everyone. Those who paid, those who sympathized, those who helped. Kill them all.”

Margarita Simonyan, head of the state-funded television channel RT, shared photos of the four men’s bruised and swollen faces on X, formerly Twitter.

She said that even the death penalty — currently banned in Russia — would be “too easy” a punishment.

Instead, she said they should face “lifelong hard labor somewhere underground, living there too, without the opportunity to ever see light, on bread and water, with a ban on conversations and with a not very humane escort.”

Russian human rights advocates condemned the violence against the men.

Team Against Torture, a prominent group that advocates against police brutality, said in a statement that the culprits must face stern punishment, but “savagery should not be the answer to savagery.”

It said the value of any testimony obtained by torture was “critically low,” and “if the government allows for torture of terrorism suspects, it may allow unlawful violence toward other citizens, too.”

Net Freedoms, another Russian group that focuses on freedom of speech cases, said Medvedev’s remarks, as well as Putin’s recent call on security services to “punish traitors without a statute of limitation no matter where they are,” made against the backdrop of “demonstrative torture of the detained … effectively authorize extrajudicial killings and give instructions to security forces on how to treat enemies.”

“We’re seeing the possible beginning of the new Great Terror,” Net Freedoms said, referring to mass repressions by Soviet dictator Josef Stalin. The group foresees more police brutality against suspects in terrorist-related cases and a spike in violent crimes against migrants.

Abuse of suspects by law enforcement and security services isn’t new, said Sergei Davidis of the Memorial human rights group.

“We know about torture of Ukrainian prisoners of war, we know about mass torture of those charged with terrorism, high treason and other crimes, especially those investigated by the Federal Security Service. Here, it was for the first time made public,” Davidis said.

Parading beaten suspects could reflect a desire by authorities to show a muscular response to try to defuse any criticism of their inability to prevent the attack, he said.

It was a major embarrassment for Putin and came less than a week after he cemented his grip on Russia for another six years in a vote that followed the harshest crackdown on dissent since Soviet times.

Many on Russian social media questioned how authorities and their vast security apparatus that actively surveils, pressures and prosecutes critics failed to prevent the attack despite the U.S. warning.

Citing the treatment of the suspects, Davidis told AP that “we can suppose it was deliberately made public in order to show the severity of response of the state.”

“People are not satisfied with this situation when such a huge number of law enforcement officers didn’t manage to prevent such an attack, and they demonstrate the severe reaction in order to stop these accusations against them,” he said.

The fact that the security forces did not conceal their methods was “a bad sign,” he said.

IS, which fought Russian forces that intervened in the Syrian civil war, has long targeted the country. In a statement posted by the group’s Aamaq news agency, the IS Afghanistan affiliate said it carried out an attack in Krasnogorsk, the suburb of Moscow where the concert hall is located.

In October 2015, a bomb planted by IS downed a Russian passenger plane over Sinai, killing all 224 people aboard, most of them Russian vacationers returning from Egypt.

The group, which operates mainly in Syria and Iraq but also in Afghanistan and Africa, has claimed responsibility for several attacks in Russia’s volatile Caucasus and other regions in past years. It recruited fighters from Russia and other parts of the former Soviet Union.