Two out of four suspects have pleaded guilty after appearing in court charged with terror offences after the concert hall attack near Moscow which killed more than 130 people.
All four suspects, from Tajikistan, have been remanded in custody until at least 22 May before facing trial, according to Russian authorities.
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Dalerdzhon Barotovich Mirzoyev, 32, Saidakrami Murodali Rachabalizoda, 30, Shamsidin Fariduni, 25, and Muhammadsobir Fayzov, 19, appeared at the Basmanny district court in Moscow on Sunday.
The number of people killed in the attack on the Piknik rock concert at Crocus City Hall Krasnogorsk on Friday night has risen to 137. At least 182 people were injured.
Mirzoyev and Rachabalizoda admitted guilt after being charged.
The fourth suspect, Fayzov, was brought to court directly from a hospital in a wheelchair.
Medical staff stayed with Fayzov while he was in court, where he wore a hospital gown and trousers. He appeared to have a number of cuts.
The other three suspects appeared in court heavily bruised with swollen faces amid reports in Russian media that they were tortured during interrogation by the security services.
Video footage showed them being dragged through the court building before the hearing.
A branch of Islamic State (IS), IS-K, has claimed responsibility for Friday’s attack. Russian authorities said the men were trying to flee to Ukraine when they were apprehended, but this is so far unsubstantiated.
Graphic video footage circulated online appeared to show some of them being apprehended by the side of a road in the hours following the concert.