Calls mounted on Monday to harshly punish those behind the Russia concert hall attack that killed more than 130 people as authorities combed the burned-out ruins of the shopping and entertainment complex for more bodies.

Four men, charged with carrying out a terrorist attack, appeared in court Sunday night and showed signs of being severely beaten.

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.

An affiliate of the Islamic State group claimed responsibility for the attack, and U.S. intelligence backed up their claims.

But Kremlin spokesman Dmitry Peskov refused to assign blame, urging reporters Monday to wait for the results of the investigation in Russia. He also refused to comment on reports that the U.S. warned authorities in Moscow on March 7 about a possible terrorist attack, saying any such intelligence is confidential.

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, but their fate 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.

The fourth suspect, Faizov, appeared in court in a wheelchair and sat with his eyes closed throughout. He was attended by medical personnel in court, where he wore a hospital gown and 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 the suspects.

“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.”

Opposition activists and human rights advocates noted “demonstrative cruelty” toward the men. 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.

“They decided that this time there are no reasons to conceal their methods,” he said, adding, “It is a bad sign.”

Anastasia Burakova, a lawyer and founder of the Kovcheg group that helps Russians who fled abroad, echoed Davidis’ sentiment, writing on X: “From these days on, torture entered the public sphere and ceased to be an unspoken practice.”

The attack 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.

Some commentators on Russian social media questioned how authorities, who have relentlessly suppressed any opposition activities and prosecuted critics, failed to prevent the attack despite the U.S. warning.

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