Four men, all of whom are citizens of Tajikistan, have been charged with committing acts of terrorism during the shocking attack on a concert hall, in Krasnogorsk, a northern Moscow suburb, which left at least 137 people dead and more than 100 injured.

They had fired indiscriminately at a section of the estimated 6,000 people who were attending a rock concert. The attackers also set fires which engulfed the venue and caused the roof to collapse.

The Islamic State, or IS, has already admitted it was their organization which carried out the 22 March atrocity at Crocus City Hall, and the quartet of suspects are believed to have been recruited by the terror group.

The four men were named by Russian authorities as: Dalerdzhon Mirzoyev, Saidakrami Murodali Rachabalizoda, Shamsidin Fariduni and Muhammadsobir Fayzov. Video shows three of the men being marched bent double into Basmanny district court, in the Russian capital, while the fourth needed a wheelchair to enter the room.

All showed signs of severe beatings; indeed more video footage was leaked showing brutal interrogation sessions by Russian security forces, and reports suggest at least one had suffered electric shocks.

Two of the suspects accepted their guilt in the assault, although the men’s condition raised questions about whether they were speaking freely.

The two were identified as Mirzoyev and Rachabalizoda, with the latter’s ear heavily bandaged from what is understood to be the result of having been partially severed during his arrest. Mirzoyev appeared to have a torn plastic bag wrapped around his neck, leaving little to the imagination as to the sort of treatment he had been subjected to.

Russian officials had claimed, without any evidence, that there was Ukrainian involvement, an accusation which Kyiv immediately refuted calling it “absurd”.

All four men are to be held in pre-trial detention until at least 22 May. Their offences if found guilty, carries a maximum life sentence.

Day of mourning

The hearing, at which all four of the men were held in a glass-panelled booth, heavily guarded by masked police throughout, came as Russia observed a national day of mourning. Events at cultural institutions were cancelled over the weekend, flags were lowered to half mast and television entertainment and advertising were completely suspended.

Deadliest in years as identifying dead continue

A statement later made public said that Mirzoyev had “admitted his guilt in full”, while Rachabalizoda also “admitted guilt”.

The face of the man identified as Fariduni was badly swollen, while the man named as Fayzov appeared to lose consciousness as he was brought into court in a wheelchair wearing a thin hospital gown, he appeared to have an eye missing.

The men had been apprehended in the Bryansk region, which is some 400km south-west of Moscow, approximately 14 hours after the attack, which is the deadliest on Russian soil in years.

Rescuers have continued to search the damaged building, as the Department of Health confirmed that it had begun identifying the bodies of those killed via DNA testing, but added that the process would take at least two weeks.