Was this an act of domestic resistance, or Ukrainian?  Opinions vary. There isn’t enough evidence to distinguish, while Russian propagandists spin fictions to serve the state.

One constant should be considered in every argument.  In 2015, several rebel commanders were  likely assassinated by the Kremlin. See Rebel Commander Aleksey Mozgovoy Killed in East Ukraine, Frozen Conflict?

This option is no longer directly available. If the Kremlin desired to use the state security apparatus to neutralize a Tatarsky, Dugin, Girkin, or Prigozhin, they couldn’t do it:

• A substantial minority, the ultra nationalists, would attempt to violently overthrow Putin.
• The security apparatus is riven. An order might be  leaked, sabotaged, or never executed.
• A program to defang ultra nationalists must not be attributable to the broader Kremlin.

Implication. If the Kremlin eliminated Tatarsky, proxies were employed. With traditional Russian skills of subversion and infiltration, proxies could even be obtained from anti-war groups. The Russian political cycle up to  1953  has numerous examples of the use of one faction or creche used to destroy another, followed by its own destruction.

The prototype is the killing of Sergey Kirov, discussed  in Juan Guaido Watch Your Back; Trump says ‘Russia has to get out’ of Venezuela Part 2.

Coincidentally, Kirov was killed in Saint Petersburg.