I think we have different definitions of "cold-blooded". the cop scenario you laid out is a situation where a good person kills a bad person to prevent that bad person from doing harm. I would agree that that scenario is justified and would even argue that it is moral.

murdering the CEO does not prevent United health from continuing to do the harm that they do. if anything, they will double down. given this, the only explanation for the murderer I can see is revenge, and that is immoral.