Image source, ReutersRussia has charged four suspects it says carried out the attack in a Moscow concert hall that killed at least 137 people.
The men were led blindfolded into a Moscow court to face a charge of committing an act of terrorism.
Islamic State has 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 them being marched by masked police into Basmanny district court in the Russian capital.
They were then placed behind a glass screen for their appearance.
Mirzoyev and Rachabalizoda's eyes were blackened and the latter's ear was heavily bandaged – reportedly from it being partially severed during his arrest.
A court statement said that Mirzoyev was named as 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.