For this monster sprite I drew and animated the torso, pelvis, BG arm, and BG leg together on the same layer as they are not interchangeable between zombies. For your particular use case there would be quite a bit of separating involved, simply because it was not designed with that in mind in the first place.
I'm not sure what exactly your use case is- Perhaps you have the zombies explode into pieces when they die? I could update this pack in the future with some alternate death effects and zombie chunks.