President Vladimir Putin declared Sunday a national day of mourning after pledging to punish all those behind the attack, in which 137 people were killed, including three children, and 182 were injured.

Over 100 people remained in hospital, some of them in a serious condition. Video footage showed a sombre-looking Putin lighting a candle at a church at his residence outside Moscow on Sunday evening to honour those who died.

Earlier on Sunday, people laid flowers at Crocus City Hall, the 6,200-seat concert hall outside Moscow where four armed men burst in just before Soviet-era rock group Picnic was to perform its hit “Afraid of Nothing”. The men fired their automatic weapons in short bursts at civilians who fell screaming.

Islamic State has claimed responsibility for the attack, but Putin has not publicly mentioned the Islamist militant group in connection with the attackers, who he said had been trying to escape to Ukraine. He said that some on “the Ukrainian side” had been prepared to spirit the gunmen across the border.

Ukraine has denied any role in the attack.

Moscow’s Basmanny district court on Sunday charged four suspects with acts of terrorism in connection with the attack, naming them as Dalerdzhon Mirzoyev, Saidakrami Rachabalizoda, Shamsidin Fariduni, and Muhammadsobir Fayzov, according to Moscow courts’ official Telegram channel.

It said the men, identified by Russian media as all being citizens of the ex-Soviet republic of Tajikistan living in Russia,would be remanded in pre-trial custody until May 22. Three of the four had pleaded guilty to all charges, it said.

After unverified and brutal videos of the suspects’ interrogations circulated on social media, courtroom images published by Russian media showed one suspect was brought in on a wheelchair apparently missing an eye, another had a bandage where his right ear should be, another had a black eye and a ripped plastic bag around his neck, and a fourth suspect with a swollen face seemed disoriented and struggling to keep his eyes open.

Friday’s attack was the deadliest on Russian territory since the 2004 Beslan school siege, when Islamist militants took more than 1,000 people hostage. More than 300 people died at the time, more than half of them children.

Dmitry Medvedev, deputy chairman of Russia’s Security Council, said Russia would target those behind the deadly shooting wherever they were from and whoever they were.

He had previously spoken of the need to meet “death with death” and some lawmakers have begun to discuss whether the death penalty should be re-introduced.

Across Moscow, billboards carried a picture of a single candle, the date of the attack and the words “We mourn”.

Countries around the world have expressed horror at the attack and sent their condolences to the Russian people.

GUNMEN

Putin said 11 people had been detained, including the four suspected gunmen, who fled the concert hall and made their way to the Bryansk region, about 340 km (210 miles) southwest of Moscow.

“They tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border,” Putin said.

Russia’s Federal Security Service (FSB) said the gunmen had contacts in Ukraine and were captured near the border.

Putin ordered a full-scale invasion of Ukraine in February 2022, something he called a special military operation needed to protect Russia and Russian-speakers in Ukraine.

Ukrainian President Volodymyr Zelenskiy has accused Putin of seeking to divert blame for the concert hall attack by referring to Ukraine.

Islamic State, the Islamist group that once sought control over swathes of Iraq and Syria, claimed responsibility for the attack in a Telegram statement from the group’s Amaq agency. On Saturday night, Islamic State released on its Telegram channels what it said was footage of the attack.

In video footage published by Russian media and Telegram channels with close ties to the Kremlin, one of the suspects said he was offered money to carry out the attack.

“I shot people,” the suspect, his hands tied and his hair held by an interrogator, a black boot beneath his chin, said in poor and heavily accented Russian.

When asked why, he said: “For money.” The man said he had been promised half a million roubles (a little over $5,000). One was shown answering questions through a Tajik translator.

Unverified footage posted to Russian Telegram channels appeared to show one of the suspects being tortured with electric shocks in detention. Reuters could not verify its authenticity.

ISLAMIC STATE

The White House said the U.S. government shared information with Russia early this month about a planned attack in Moscow, and issued a public advisory to Americans in Russia on March 7. It said Islamic State bore sole responsibility for the attack.

“There was no Ukrainian involvement whatsoever,” U.S. National Security Council spokesperson Adrienne Watson said.

Russian officials have bristled at the U.S. public comments on the attack, the first of which were made shortly after news of the attack had broken, and say Russian investigators must be allowed to make their own findings.