So the supreme court already ruled the president cannot be held accountable for anyone they kill.
The vice president becomes the president instantly if the president dies.
What is preventing any vice president from waiting until day 1 of their parties presidency, and then murdering the president? And then instantly pardoning themself?
I believe the VP only becomes “acting President” and doesn’t assume the actual office until sworn in by a proper authority (usually the Chief Justice of SCOTUS but I believe contingency plans exist). So it would be interesting to figure out when the immunity attaches.