Russia has charged four men it says carried out the attack in a Moscow concert hall that killed at least 137 people.
The suspects were marched blindfolded into a Moscow court to face a charge of committing an act of terrorism.
The Islamic State group said it carried out Friday's outrage at Crocus City Hall, and posted video from the attack.
Russian officials have claimed, without evidence, Ukrainian involvement. Kyiv says the claim is "absurd".
The men appeared in court on Sunday.
They were named as Dalerdzhon Mirzoyev, Saidakrami Murodali Rachabalizoda, Shamsidin Fariduni and Muhammadsobir Fayzov.
Video showed some of them being marched blindfolded by masked police into Basmanny district court in the Russian capital. All appeared to have been injured.
Mirzoyev and Rachabalizoda's eyes were blackened and the latter's ear was heavily bandaged - reportedly from it being partially severed during his arrest.
Fayzov was brought into court in a wheelchair and appeared to have an eye missing, according to the Reuters news agency. Fariduni's face was badly swollen.
A court statement on the Telegram messaging service said Mirzoyev was a citizen of Tajikistan and "admitted his guilt in full". Rachabalizoda, whose nationality was not disclosed, also "admitted guilt", it said.
All four are to be held in detention until at least 22 May, the court added.
- This story was first published by BBC