If a terrorist takes hostages and starts shooting them one by one, surely a sniper bullet would be justified to save the lives of those hostages.
For you, it’s just animus towards the victim who is “a prick.” For the rest of us, he’s a for-profit murderer for whom our stock market rewards and celebrates. There will never be a court of law that brings people like him to justice let alone to stop him from committing more murders. I’ll never pull the trigger myself but until there is a such court of law, I’ll take the court of public opinion when someone is brave enough to rescue us hostages.