It's true. In many states, you are guilty of assault if you threaten someone sufficiently, even if you had no intention of carrying out the threat. It's true for a number of violent crimes.

Not sure why the GP got downvoted for stating facts, though I don't know the details of the murder-for-hire plot, so perhaps it somehow doesn't pertain in that particular case.

Regardless, it's a legit thing. So be careful about threatening people with bodily harm.