How did Dan Scott get away with killing Nanny Carrie on OTH?

Deb and Haley saw him shoot her once...but after we see him shoot her again and kill her. So, if Haley and Deb knew that he hadn't killed her (at the very least we know that they only saw him shoot her once), how did he get away with actually killing her? When she wakes up when Dan's waiting for the police, she threatens him and he kills her. Dan was on parole at the time, So I guess what I'm wondering...were Deb and Haley aware that he hadn't killed her with the first shot? I've been rewatching older episodes and all of these new questions have been rising...lol Give me your intakes...