Once Callie, as a medical professional, started CPR she would not have stopped until the ambulance arrived and she was relieved of duty. A medical professional who stops care once started could then be charged for abandonment.
Callie, who is a nurse studying to be a doctor, starts administering CPR, but doesn't bother to check if the victim's airway is obstructed (step 1), plus it's very clear that he has a bullet wound yet she does nothing to stop the bleeding.
The medical examiner claims that "according to the projectile and the casing at the scene, it was a .38 that killed him. Lol a .38 is a revolver (yes, there are a few .38 automatics but they are rare), and revolvers do not eject their spent casings. No one would have taken the time to open the cylinder and remove one spent casing. Also, without actually having dug the bullet out of the corpse-which is never done at the scene- and measured it, how would he know the caliber.