There are no “magic words” that make a threat legal. It’s always a question of context.
For example if Don Corleone came to your business and said “Nice place you got here, would be a shame if it burned down. By the way I happen to sell fire protection”, that would absolutely be illegal even though he never said he would do anything wrong. The intent is clear to all.
So it doesn’t really matter if someone says “I wish that guy was dead!” vs “I’m going to kill that guy!” Either one can be an illegal true threat, or not, depending on the context.