Does it sound like a sociopath wrote it?
Dearest Amy,
Hello Amy. I sort of . . . popped in on you and Josh. Bravo on getting over what your father did to you. Now, onto more important matters, I’ve noticed that you haven’t approached Josh about the first letter. Do you think I’m just a joke? Well, you’re wrong Amy, dead wrong. If you’re smart you’ll skip town or tell Josh about the letters.
Do you want to die that badly? Tonia thought I was joking, that I was never going to hurt her. She was as wrong as you are. She lost her life because of her stupidity! Either get out or start planning your own funeral.
Well, looks like I lost my temper there for a minute. I apologize. But I’m warning you, if you’re not gone before Thursday I will have to do something about it.
With Love,
Art

Wow! Not bad
Although, I wouldn’t call this a scene lol. Very nice.
Sounds like it to me…the person Art may be admitting to a past murder as well…don’t even answer that person let police take him in for questioning…
It is good. The best line showing he’s a sociopath is “Bravo on getting over what your father did to you.” Her father abused her and Art walked in on her and josh making out, right? It’s a great line. However, I think Art should emotionally threaten her more. For example, talk about how so-and-so would be lost without her if she died. Talk about the pain it would bring others if they were the ones to stumble across her dead body.