Another possibility is that he may have only found her phone in the pocket of her tracky pants when he was out at Kholo Creek - and suddenly realized that it could have had location services switched on and tracked the entire journey. So maybe he grabbed it before rolling her off the bridge, then got rid of it on the way home? Just another vague possibility.
KG1 - all sorts of stuff can be recovered from a found phone, especially an iPhone which is what Allison had. And especially if she had tracking apps on there such as "Find My Friends" - which GBC had on his. He said he used it, but he didn't - the judge commented that he must have been stupid to say he used it when he hadn't. But Allison's may have been running, so the track would have been recoverable. Also any texts including the ones he sent that morning, but which we only presume got to Allison's phone - we don't actually know that. As they both had iPhones, the messages could have gone via iMessage and not via the phone system at all.
Also Allison's Contacts list, her Calendar, her Notes if she used them.
Now presumably the Police could have got a lot of that stuff from the home computer that Allison used to sync her phone to - it stores backups. So whatever was on there that could have been incriminating would presumably have been something that occurred after the last sync.
And of course we know that details such as phone going on and off charger are logged.
Lots more too, especially with that Cellebrite software that is used by Forensic techs.
