I'm trying to understand your question.
Are you asking whether the boyfriend should be charged in Taylor's death, because his actions led to the events that resulted in her death?
-PJ
No.
Actual situation: cop goes into room, botfried shoots, cop shoots back, accidentally kills Breonna. Cop not guilty; shooting was self defense against boyfriend.
Hypothetical: non-police citizen goes in, gets into argument with boyfriend,say, boyfriend shoots, man shoots back, accidentally kills Breonna. The shooting is still legit self-defense, but now Breonna was killed by a non-police officer.
Does the same law that shielded the cop, above, from liability in killing Breonna also shield the non-cop shooter, below, who also accidentally killed Breonna?