My friend is talking about suicide a lot, how do I tell his Ex-GF to quit messing with him?

She is always sending him messages telling him, hes worthless, he'll never get anyone else,and that he should die and other things. Hes been talking about suicide now. How can i her to leave him alone? Isn't her telling him to kill himself some kinda crime? Accomplice to Suicide? I don't know, I just want to say something to scare her into not talking to him anymore.