While The SUN(!) quotes a tweet from one NATO-hack with the novel theory that PuTiN dId It!!!, real media report that FSB is on the case hard and heavy.

The FSB reported on the identification of the customers and perpetrators of the murder of Daria Dugina.

The murder was planned by the Ukrainian special services.
The direct perpetrator of the murder was a citizen of Ukraine Natalia Vovk, born in 1979, who left Russia for Estonia on August 21.

It’s hard to imagine, though not entirely impossible, that SBU can operate in Russia without SIS/CIA assistance or direction. So, as justice is prepared and served, it might be sufficient to just avoid Langley, SIS HQ, and Volodymyrska Street, Kiev.