Four suspects accused of killing more than 130 people in a terrorist attack at a Moscow concert hall appeared heavily beaten as they were charged by a court in the Russian capital Sunday.

Photos and videos released by the court showed the four men being led into the courtroom with various levels of injuries. Three of the men had visible bruises and swelling on their faces, including one with heavy bandaging around his right ear. The fourth seemed barely conscious as he sat inside the prisoner’s box dressed in a hospital gown and on a stretcher, with his eyes closed for most of the hearing.

It came after images showing the suspects’ violent treatment in custody were shared widely across Russian social media, and as President Vladimir Putin vowed revenge but made no mention of the Islamic State group, which claimed responsibility for the deadly attack.

The Basmanny District Court of Moscow named the suspects as Dalerdzhon Mirzoyev, Saidakrami Rachabalizoda, Shamsidin Fariduni and Mukhammadsobir Faizov. Two of the four had admitted their guilt, the court said, although their condition raised questions about whether they were able to speak freely.

All four were charged with committing a terror act, according to the court, and could face up to life imprisonment. The suspects were ordered detained until May 22 by the court. Seven more people were detained on suspicion of involvement in the attack.

All four are citizens of ex-Soviet state Tajikistan, Tass state news agency reported. The suspects had to use a translator to communicate in court, according to Tass.

NBC News analyzed footage shared over the weekend by Russian pro-war Telegram channels that showed at least one of the suspects being tortured, and others violently interrogated and injured. NBC News was able to authenticate the footage by comparing it with images of the suspects as they appeared in court on Sunday.

In one video, suspect Saidakrami Rachabalizoda lies on the ground in the woods while a man hacks at Rachabalizoda’s ear with a knife, before stuffing what looks like part of the ear into Rachabalizoda’s own mouth. Videos also show suspect Shamsidin Fariduni being interrogated on the ground in the woods as a man holds Fariduni’s head up by his hair. In a subsequent image, Fariduni drools on the floor of a sports hall with his pants and underwear around his knees while a man stands on his leg, a black box at his side.

The men are accused of perpetrating the worst terror attack Russia has seen in the last 20 years, killing at least 137 people and leaving dozens injured. Videos from inside the Crocus City Hall on Friday night showed several armed and camouflaged men shooting at people inside the venue, seemingly at random. The venue also caught on fire after an alleged explosion, leading the roof to cave in.

The detention hearing for the four suspects came as Russia marked a national day of mourning Sunday, and people continued to bring flowers to the burned-out site of the attack.

Putin claimed Ukraine’s involvement in preparing an escape route for the suspects before they were captured, an accusation Kyiv has vehemently denied and said was being used to distract from his own security failings and raise support for intensifying his military campaign.

In a sign of the febrile mood among Russian officials and beyond, a leading Kremlin propagandist offered an approving nod to the signs of torture and others called for the perpetrators to face the most severe punishment, with some even reviving calls to bring back the death penalty.

“I never expected this from myself, but when I see how they are brought into the court crooked, and even this ear, I feel extremely satisfied,” the head of the Russian state broadcaster RT, Margarita Simonyan, said on Telegram, next to the images of the four suspects from the court.

Meanwhile, former president and deputy chairman of Russia’s Security Council, Dmitry Medvedev, called Monday for the perpetrators and everyone involved in facilitating the attack to be killed. “Who paid, who sympathized, who helped. Kill them all,” he said in a post on Telegram.

Putin himself indicated in his address to the nation Saturday, nearly a day after the attack, that there would be no mercy for those behind what he called the “bloody massacre.”

“Terrorists, murderers, non-humans who do not and cannot have a nationality face one unenviable fate — retribution and oblivion,” said Putin, who less than a week ago was jubilantly celebrating his choreographed landslide election win.

Kremlin spokesperson Dmitry Peskov declined to comment Monday when asked about the signs of violence on the suspects’ faces during their court appearance and the videos of alleged torture circulating online.

The Russian defense ministry said Monday that border servicemen who helped detain the four suspects in the Bryansk region, near the borders with both Ukraine and Belarus, received state awards for their bravery.

4 Men Charged in Moscow Terror Attack That Killed at Least 137 People. Here's What to Know

A Russian court charged four men with terrorism on Monday after an attack on a Russian concert hall on Friday night killed at least 137 people, making it the deadliest terror attack in the country in two decades.

Over 100 people remained in hospital, some of them in a serious condition. Islamic State has claimed responsibility for the attack.

Three of the four suspects—Dalerjon Mirzoev, Saidakrami Rachabalizoda, Muhammadsobir Fayzov, and Shamsidin Fariduni—pleaded guilty to all charges, according to Moscow courts’ official Telegram channel. The men are citizens of Tajikistan and will be placed in pre-trial detention facilities until May 22, according to Russian courts.

After unverified videos of their interrogations circulated on social media, courtroom images published by Russian media showed one suspect brought in by wheelchair with a missing eye, another with a bandage where his right ear should be, another with a black eye, and a fourth with a swollen face, Reuters reported.

Here is what to know about the attack.

Who is responsible for the Moscow attack?

A U.S. official who spoke to the Washington Post on condition of anonymity said there was “no reason to doubt” Islamic State’s claim of responsibility for the attack. While Islamic State has not said which of its branches is responsible, U.S. officials believe ISIS-K, a branch based in the Khorasan Province of South-Central Asia and is active in Russia, is behind the attack.

Islamic State has claimed responsibility for previous attacks on Russian civilians, including the bombing of a commercial airplane flying from Sharm-el-Sheikh, Egypt to St. Petersburg in 2015 that killed 224 people.

How has Russia responded?

The attack came just days after Russian President Vladimir Putin declared victory in the country’s presidential election, which was called “preordained” by the Associated Press.

Putin vowed to punish those responsible.

“The criminals in cold blood, purposefully went to kill and shoot at point-blank range our citizens and our children, as the Nazis did who committed massacres in the occupied territories. They planned to stage a demonstrative execution, a bloody act of intimidation,” he said in a televised speech after the attack. “All perpetrators, organizers, and sponsors of this crime will be fairly and unavoidably punished, whoever they are or whoever directs them.”

Putin did not refer to the Islamic State in his public address following the attack and said the accused were “moving toward Ukraine” before being caught and that “a window was prepared for them from the Ukrainian side to cross the state border.”

Ukraine has strongly denied any involvement in the attack. “Ukraine certainly has nothing to do with the shooting/explosions in the Crocus City Hall (Moscow Region, Russia). It makes no sense whatsoever,” wrote Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelensky, on X shortly after the attack.

Russia held a day of mourning on Sunday with a memorial outside the concert hall.

Multiple Russian lawmakers have called for reinstating the death penalty in the country for the attackers. A moratorium on the death penalty was established by former President Boris Yeltsin in 1996, and Russia has not carried out executions since then.

Missed warnings from the U.S.

Earlier this month, the U.S. government issued an advisory to American citizens in Russia warning of a planned terror attack in Moscow that would target large gatherings like concerts. The warning was based on intelligence suggesting that ISIS-K was engaging in activity inside Russia. The U.S. shared this information with the Russian government as part of its “duty to warn” policy, National Security Council spokeswoman Adrienne Watson said in a statement on X.

The Kremlin dismissed the warnings as American propaganda and said that they were an attempt to meddle in the Russian election.