No, I believe the LE is claiming RN deleted it when she listened to it at 12:50 am. I guess that sentence was not very clear, I meant they turned the phone on August 15 to learn that the voicemail was deleted and they couldn't recover it since it's been a month and AT&T doesn't keep it on their servers for more than one week.
LE does believe RZ deleted the voicemail on July 13.
LE initially did not want to access the phone manually because doing so can overwrite deleted data in the memory. They claim they waited while they attempted to find software that could forensically download and save all the data on the phone.
They initially were not successful in finding the software, however, so they powered up the phone manually Aug 15 and only then did they discover the voicemail (which JS had told them about) was deleted.
This past week, however, LE suddenly reported that detectives have located the correct forensic software and/or hardware to examine the phone. This, two months after RZ's death. Currently, they are in the process of their forensic exam.
Wiki on cell phone forensics:
[ame="http://en.wikipedia.org/wiki/Mobile_device_forensics"]Mobile device forensics - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:RF_bag_with_iPhone.jpg" class="image"><img alt="" src="http://upload.wikimedia.org/wikipedia/commons/thumb/6/69/RF_bag_with_iPhone.jpg/220px-RF_bag_with_iPhone.jpg"@@AMEPARAM@@commons/thumb/6/69/RF_bag_with_iPhone.jpg/220px-RF_bag_with_iPhone.jpg[/ame]