A Khabarovsk court said one suspect was remanded in absentia after Tuesday's blast in the far-east region killed one lieutenant colonel and injured several others.
Russian and Ukrainian media and military bloggers said the apparent target was Major General Azatbek Omurbekov, the sanctioned former commander linked to atrocities in Bucha.
Ukraine has not commented. If confirmed, the case would add to a series of attacks on senior Russian military and security figures, including shootings and car bombings in Moscow.
Are internal security failures becoming a greater threat to Putin's regime than the Ukrainian frontline?
As Russia builds a police state, why can't its security services protect high-value targets from assassins?