Doesn’t matter whether the person knows personally his/her target.
Again, I didn’t see anyone said anything about killing someone, but if found true and depending the context, you can be in legal trouble.
https://blogs.findlaw.com/blotter/2016/10/is-it-illegal-to-threaten-someone-online.html
https://answers.uslegal.com/criminal/16784/
and there many more cases, real cases, where people get in legal troubles.
If I report/tip to local/state/federal law enforcement agencies for someone’s verbal abuse and threat to physical harm to a specific target, you can bet you’d see FBI knocking your door real fast.