Nineteen people, among them the four suspected gunmen, went on trial in Moscow on Monday over a concert hall attack that claimed 149 lives, one of the worst terrorist attacks in modern Russia.

Four armed men from the former Soviet republic of Tajikistan allegedly stormed the Crocus City Hall on the outskirts of Moscow on 22 March last year, opening fire and then setting the building alight, injuring hundreds of people.

Isis-K, the Islamic State affiliate active in central and south Asia, claimed responsibility for the attack. Moscow, however, has alleged – without presenting credible evidence – that the attack was carried out “in the interests” of Ukraine.

The four suspected attackers and another 15 people accused of being accomplices appeared in court on Monday. About 30 survivors were also present. A military court opened the case behind closed doors, with additional hearings scheduled for later this week.

The attack shocked Russia and was widely seen as the result of a catastrophic security failure, with the country’s security services distracted by the war in Ukraine and a crackdown on domestic anti-war dissent.

In the weeks before the assault, western intelligence agencies had privately and publicly warned Moscow of “imminent plans to target large gatherings” in the city. But just three days before the attack, Putin dismissed the warnings as “an attempt to scare and intimidate our society”.

Nearly half of the victims were killed by smoke and carbon monoxide inhalation from the fire that broke out, not from gunfire, the state TASS news agency reported on Sunday, citing case materials.

The four men accused of having carried out the gruesome murders were identified as Saidakrami Murodali Rachabalizoda, Dalerdzhon Barotovich Mirzoyev, Shamsidin Fariduni and Muhammadsobir Fayzov.

Human rights groups have criticised Russia’s treatment of the suspects, noting that when the men first appeared in court shortly after the attack, there were clear signs of torture. A video published online at the time of their arrest showed one of the captives – apparently in the custody of Russian military personnel – having his ear sliced off and forced into his mouth, while being ordered to eat it.

The men had reportedly been living in Moscow and its surrounding areas, part of the roughly 1.5 million Tajik migrants who have left the poverty and unemployment of their home towns and villages in search of a better future in Russia. They were apparently then recruited and radicalised by Isis-K.

The attack has fuelled a new wave of anti-migrant sentiment across Russia, with central Asian migrants increasingly being subjected to police searches and arrests, and in some cases, forcibly conscripted to fight for Russia in Ukraine.

Despite overwhelming evidence that Isis-K was solely responsible, Russia has repeatedly sought to implicate Ukraine and the west in the attack.

“This inhuman crime was planned and committed in the interests of the current leadership of Ukraine in order to destabilise the political situation in our country,” Russian investigators said in a statement last month.

Kyiv has called these allegations baseless and absurd.

The head of Russia’s FSB security service, Alexander Bortnikov, previously said that he “believes” the US, Britain and Ukraine were behind the attack.