The Russian Federal Security Service (FSB) released a statement detailing the arrest of three additional men, who the FSB claim were responsible for the terrorist attack on the Crocus City Hall in Krasnogorsk, Russia on March 22. Over a dozen others have already been arrested in connection with the attack, which resulted in the death of over 140 people.

Of the three men the FSB arrested on Thursday, one was a Russian citizen, the other two were foreign nationals. The FSB claimed that all three traveled to Russia specifically to assist in the attack. The Russian citizen was allegedly in charge of recruiting other individuals to assist in the attack, while the other men financed the operation and purchased firearms and vehicles used in the attack. All three were arrested in separate cities but knew of each other’s involvement.

The attack, which killed over 140 people, was the deadliest in the past 20 years of Russian history. The terrorist group ISIS claimed responsibility for the attack, claiming it was targeted at Christians gathered within the venue.

The FSB also claimed that the men arrested confessed that they were in the process of planning further attacks on Russian soil. Since the attack, the FSB claims to have thwarted more than five additional terrorist plots.

The FSB has also had to deal with concerns that “copycat” attacks will come about due to the publicity that the recent attack has garnered. In a statement, they warned Russians that there is a chance that many people who feel ostracized by the government and its actions may use these attacks as a rallying cry. The FSB warned Russians to respond vigilantly to these potential threats to prevent panic from taking hold.

Russia is under increased international scrutiny due to the recent death of opposition leader Alexei Navalny and the ongoing war in Ukraine. Relatedly, the FSB also asked that any countries sheltering those associated with the Crocus City Hall attack turn over the suspects, including Ukraine.