Eh?
I assume the reference is to the scene where Greene is alone in the lift with a patient who was some criminal or something, I forget precisely what; said patient crashed and Greene discharged the defibrillator into the air to make it look like he was attempting resuscitation. "cold blooded killer" is a tad strong. Malpractice, certainly, but the person who
shot the patient killed him. Greene simply didn't save him.
But surely since Greene is a doctor, he has the duty to save a patient - ANY patient? If you have the power to save someone, but do nothing, and the patient dies, you are therefore the ultimate cause of the patient's death. The shooter only wounded the victim; death only occurred because of Greene's inaction. Therefore Greene essentially killed him. Greene, as a doctor, is NOT ALLOWED to make judgments like this. He is obligated to save all patients. Whether they be saints or criminals. Therefore in this instance, Greene WAS a killer.