Yeah, that’s concerning. It sounds like the kid has a “troubled home life.” He’s not coming up with these ideas on his own. I’d suggest calling CPS. They’re notoriously incompetent, but they’re the people that are supposed to handle this sort of situation. Sometimes they actually do good work. Make sure you file your report anonymously. Include the information you have given here, but don’t accidentally doxx yourself or your daughter.
Please don’t take violence and subsequent threats of lethal violence as anything but.
Oh, and check out Gavin DeBecker’s The Gift of Fear and Protecting the Gift books. Trust your instincts.