I found this interesting regarding the timing of the blocked and unblocked phone calls Avery made to Halbach on the day she was murdered
"Phone records show three calls from Avery to Teresa's cell phone on Oct. 31," says Kratz. "One at 2:24 [p.m.], and one at 2:35 - both calls Avery uses the *67 feature so Teresa doesn't know it him...both placed before she arrives.
"Then one last call at 4:35 p.m., without the *67 feature. Avery first believes he can simply say she never showed up.so tries to establish the alibi call after she's already been there, hence the 4:35 call. She will never answer of course, so he doesn't need the *67 feature for that last call."
Again, doesn't directly prove anything, but is definitely a bit suspicious.