Scores of people at a concert were gunned down on Friday night in the deadliest attack inside Russia for two decades.
Vladimir Putin declared Sunday a national day of mourning after vowing to punish all those behind the attack.
At least 137 were killed, including three children, and 182 injured.
Four men accused of opening fire on crowds were forced into a courtroom on Sunday bloodied and bruised.
Putin’s security services had earlier released gruesome footage of their interrogations.
More on the Moscow attack
One shocking clip showed a suspect having his ear cut off and then force-fed back to him.
In another, one suspect appeared to be missing his eye and was covered in blood.
Meanwhile, a third man was filmed tied up and shivering near a forest as interrogators shouted questions at him.
Another man was given electric shocks to his genitals as he foamed at the mouth.
Images from a Moscow district court showed one of the suspects sitting in the defendant’s cage with a bandage on his severed ear.
Courtroom pictures published by Russian media also showed another suspect brought in on a wheelchair apparently missing an eye.
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.
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.
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.
So far 11 people have been detained, including the four suspected gunmen, who fled the concert hall and made their way to the Bryansk region, about 340 km southwest of Moscow.
In light of the attack, France has raised its terror alert warning to its highest level.
Prime Minister Gabriel Attal said the decision, which comes months before Paris hosts the Olympic Games, was taken “in light of the Islamic State’s claiming responsibility for the attack and the threats weighing on our country”.
France’s terror alert system has three levels, and the highest level is activated in the wake of an attack in France or abroad or when a threat of one is considered to be imminent.
It allows for exceptional security measures such as stepped-up patrols by armed forces in public places like train stations, airports and religious sites.
Putin has cruelly and baselessly attempted to link the slaughter in Moscow to Ukraine, claiming the suspects were heading towards Ukraine when they were captured.
Ukrainian leader Volodymyr Zelensky branded the tyrant a “low-life b*****d” for trying to shift the blame onto Kyiv.
Zelensky said it was “absolutely predictable” that Putin would seize the moment of national horror to point the finger at Ukraine.
On Friday night, Russia was hit with its worst terror attack in 20 years and the deadliest in Europe to have been claimed by ISIS.
At least 137 were killed when four gunmen stormed Crocus City Hall on Friday night and opened fire on the crowd before setting the venue ablaze.
Russian officials expect the death toll to rise further, with more than 100 wounded in hospital.
But arrogant Putin had ignored British and US warnings of a major terror attack.
Western intelligence agencies told Russia of an imminent IS threat two weeks before Friday’s horror.
Putin received the intelligence on March 7 — the same day terror suspect Shamsuddin Fariddun was seen on a recce at the concert hall.
A photographer taking pictures of visitors snapped the fiend, from Tajikistan, and later recognised him on TV.
A day later, it was revealed the US and UK embassies had issued warnings of an attack on “large gatherings” in Moscow.
Analysts believe it caused the terrorists to delay their plans.
But three days before the attack on the concert in the western Krasnogorsk suburb of Moscow, arrogant Putin said of the warnings: “It resembles outright blackmail and the intention to intimidate and destabilise our society.”