Russian security service claim to have identified killer of Darya Dugina lacks credibility

Who set the car bomb in Alexander Dugin's car?

Ukraine's "false flag" accusation seems implausible to me. A Russian false flag operation would not target Putin's friend, or the friend's daughter.

Russia's claims about a Ukrainian underground bomber seems implausible to me, for the reasons stated in the article. They make more sense as disinformation.

That Ukraine did it in some other way is less implausible, but Ukraine generally targets things that support Putin's war effort, and for good reason. Why risk inspiring disapproval by attacking a civilian?

The underground anti-Putin group possibility seems more plausible than those.