The deadly assault on a sprawling shopping and entertainment venue on the outskirts of Moscow has shocked Russians, with large crowds laying thousands of flowers at the site of the attack over the weekend and President Vladimir Putin promising to exact justice for what he said was a “cynically planned” and “barbaric” terrorist attack.

Four suspects have been arrested, Putin said, and the Islamic State — also known as ISIS — has claimed responsibility for the attack. Here’s what we know so far.

The facts

• At least 137 people were killed in Friday’s assault, when gunmen armed with automatic weapons opened fire at Crocus City Hall, a crowded concert venue that later partially collapsed after the assailants set it on fire. The incident has been described as the worst terrorist attack to hit Russia in 20 years.
• Four men — named as Dalerjon Mirzoev, Saidakrami Rachabalizoda, Muhammadsobir Fayzov and Shamsidin Fariduni — were charged with committing a terrorist act and face life in prison, Russian news agency Ria Novosti reported. Video released by the Investigative Committee showed suspects being led blindfolded into a Moscow court Sunday night.
• A U.S. official, speaking on the condition of anonymity to discuss sensitive information, told The Washington Post that the United States had “no reason to doubt” the claim of responsibility from the Islamic State. The assault came after the U.S. government issued warnings to Americans in Russia — and to Russian authorities — this month about a “planned terrorist attack” in the capital.
• The attack occurred just days after Putin’s victory in a highly orchestrated election, which solidified his power as the war in Ukraine drags into a third year.

The victims

The identities of the 137 known victims have yet to be released, but Russia’s Investigative Committee said Sunday that 62 have been identified.

At least 182 people were injured, including 101 who were still hospitalized Sunday night, the Health Ministry for the Moscow region said.

Baza, a Telegram channel with ties to Russian security services, reported that 28 bodies were found in one of the venue’s bathrooms, which included “many mothers” holding their children, while 14 others were found in an emergency exit stairwell. The Post could not immediately verify those claims.

The ISIS link

Putin did not refer to the Islamic State during his Saturday address despite its claim of responsibility, and instead asserted that the accused were “moving toward Ukraine” before they were caught, saying that “a window was prepared for them from the Ukrainian side to cross the state border.” Kyiv denied any involvement.

Though the Islamic State did not say which offshoot was responsible for the attack, Russia faces a multipronged threat from the extremist group. The U.S. warning was based in part on intelligence reporting about the possible activity inside Russia of the Islamic State-Khorasan, the Afghanistan and Pakistan arm of the group, two U.S. officials speaking on the condition of anonymity told The Post.

Writing in Foreign Policy magazine last year, three security experts argued that Russia is a “familiar enemy” for ISIS-K because of its legacy of the Soviet-Afghan war, Russia’s military tactics in Chechen wars, and its military intervention in support of Syrian President Bashar al-Assad. “By instigating jihadists to attack Russia, IS-K is looking to generate momentum, especially at a time when the core Islamic State organization in Syria is reeling from aggressive U.S. counterterrorism efforts,” they wrote, using another abbreviation for the group.

In 2015, a new offshoot, the Islamic State-Caucasus, cropped up, with militants in the Russian provinces of Dagestan, Chechnya, Ingushetia and Kabardino-Balkaria pledging allegiance.

The Islamic State also has a presence in Central Asia. Footage broadcast by Russia’s state media shows at least one of the alleged attackers speaking in Tajik during an interrogation. Tajikistan borders Afghanistan.

Douglas London, a former senior CIA officer who specialized in counterterrorism, said Russia has not prioritized the Islamic State threat emanating from this region. “Thousands of Central Asians joined the Islamic State, and many returned from Syria and Iraq after the loss of the caliphate,” he told The Post. Putin had declared victory over the Islamic State in Syria in 2017.

Reaction from Russia

Russia observed a day of mourning Sunday, with people leaving flowers at a memorial outside the concert hall. Billboards and makeshift memorials appeared in cities across the country with the words “we mourn.”

Putin, in his speech, appeared to blame Ukraine by referring to “Nazis,” a label he uses for the Ukrainian government. He made no reference to the Islamic State, nor did he address U.S. officials’ assessment of the group’s likely involvement.

Others were more forthcoming in their accusations and threatened harsh retaliation.

“Let’s give the civilian population of Ukraine 48 hours to leave the cities and finally end this war with the victorious defeat of the enemy. Using all forces and means,” Russian oligarch Konstantin Malofeev wrote Friday on Telegram.

Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelensky, dismissed the charges of Kyiv’s involvement. Ukraine “certainly has nothing to do with the shooting/explosions,” he wrote on X, adding that “everything in this war will be decided only on the battlefield.”

On Sunday, France raised its terrorism alert to the highest level over the Islamic State’s claim of responsibility for the attack, Prime Minister Gabriel Attal announced.

Catherine Belton and Robyn Dixon contributed to this report.