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, according to the BBC.

Contact us at letters@time.com.