A court in the Russian capital, Moscow, on Sunday, March 24, ruled that four people arrested on suspicion of an attack on a music hall in Moscow will remain in police custody pending trial.

At least 137 people were killed in this attack.

In the announcement of the court of Basmani district of Moscow, it was said that four people have been charged with terrorism and if they are found guilty, they can be imprisoned for life.

The court also said that these people are citizens of the Republic of Tajikistan of the former Soviet Union, who lived in Russia. The court ordered that these people will be imprisoned until May 22 of this year, and three out of four of them have pleaded guilty to all the charges.

In Russia, there was a national mourning on Sunday due to the attack on a music hall near Moscow on Friday, in which more than 137 people were killed and more than 180 were injured.

Russia’s Ministry of Public Health said rescue teams were still searching for survivors in the burning building as many families still do not know if their loved ones were killed in the attack or are still alive.

The Ministry also said that hundreds of people stood in long queues in Moscow to donate blood to those injured and burned in this attack.

Friday’s attack was the deadliest in Russia since 2004, when Islamist militants took more than 1,000 people, including students, hostage at a school.

Eyewitnesses said that the attackers were four people with automatic weapons and opened fire on people in the music hall.

The Islamic State or Daesh group claimed that they carried out the attack. The group also posted a video on Telegram that it claimed was recorded by the attackers at a music hall in Moscow.

Russian President Vladimir Putin, in his address to the nation on Saturday, expressed his condolences to the families of those killed and injured in this incident and declared Sunday as a day of national mourning in the country.

Mr. Putin also said in his speech that 11 people were arrested in connection with the incident, including four gunmen. Putin said that these people were trying to escape to Ukraine.

The Federal Security Service of Russia also claimed that the militants had connections in Ukraine and were arrested near the common border of the two countries.

But on the other hand, President of Ukraine Volodymyr Zelenskiy rejected these claims of Mr. Putin and said that Putin and his group are trying to blame others for this attack.