They will join the four alleged attackers behind bars.
The placement in pre-trial detention of three suspects in the attack which left more than 130 dead in the suburbs of Moscow was requested on Monday by Russian investigators, the court in charge of the case said.
“Three files have been received,” said the Basmanny court in the Russian capital.
According to the Ria Novosti news agency, it concerns a father and two of his sons.
Authorities announced Saturday that they had arrested a total of eleven people, and it was not immediately clear whether these three individuals were among them or not.
The profile of the suspects remains unclear
The four alleged perpetrators were placed in pre-trial detention on Sunday after their appearance in court in the capital.
Their detention, set until May 22, may be extended pending their trial, the date of which has not yet been set.
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Moscow attack: the four alleged attackers placed in pre-trial detention for “terrorism”
The authorities did not provide details on the profile of the other suspects arrested.
Asked about this by journalists on Monday, Kremlin spokesperson Dmitry Peskov did not respond.
The massacre committed Friday at Crocus City Hall, in the suburbs of Moscow, left at least 137 dead.
It is the deadliest attack on European soil claimed by the jihadist group Islamic State (IS).