They have the phone -
it was found in the area of the bodies.
So, IF this is true that the phone was in the “area” of the bodies, and not on the person of a body, that tells me that the phone may not have been easily/quickly located by a perp trying to quickly flee the area. Say, if it had slid under some brush or leaves during the attack.
And IF BG had no reason to believe his image was captured...if he was looking down, and if Libby was subtle enough, IMO that is a possibility. As far as the audio...same thing. I don’t think it’s likely it would have occurred to him that his voice was recorded. If Libby had been speaking on the phone, then yes, he might fear someone could hear his voice (or recording of his voice if she was leaving a message).
On top of the possibility of her phone not being easily located by BG, as he prepared to exit crime scene, perhaps he didn’t have a big motivation to find and take the phone either.
It seems that the motive of most murders/abducters who take a phone have the following reasons:
1. So as not to give the location of the victim away ~ (well, in this case, it doesn’t seem that he was trying to hide the location of the victims. More likely, he was just trying to “hide” the act of the crime itself, until he could disappear.)
2. So as to not leave any DNA evidence. ~ (well, if he never come into contact with the phone this would not be a concern)
3. So as to not allow the victim(s) a way to call for help. (Well, this was not a concern as victims were diseased).
I’m just offering up a possible reason for it not being a big deal, in BG’s mind, for leaving behind a cell phone. Obviously, in hindsight, he can see in fact it was a big deal. Even if his image or recording of voice does not lead to his capture, Libby’s video and audio recording could help in cracking this case, because I believe the case has received a significant increase in attention for the sole reason that the perp was caught on video by the victim(s) just prior to attack. Making this case very unique and capturing the interest of many who may have otherwise not paid much attention to this case.