Tahoe27 wrote: Anything is possible...
That's what I mean, we don't even know what he meant by the knife breaking. He said "I plunged the knife into her and it broke", but then goes on to say "I then finished the job by cutting her throat".
So, if it did break, it wasn't broken bad enough to stop him from cutting her throat with it. I'm guessing it was a small pocketknife he used. I've had them "break" where the blade doesn't lock anymore, just flops back and forth, that might be what he meant. He could have also opened another blade and used it to "finish the job".
Whatever the case, I agree it's most likely it didn't break off in her body and if it broke and fell to the ground I can't see him spending time to fish around in the dark to find it.