Here is an additional thought.
The instructor whose team found the body said that when he confronted Armstrong before they went into the water to find the girl, Armstrong's equipment was "bone dry." He had trouble understanding how your equipment could be bone dry if you had just been in the water conducting a class and then searching for a missing diver.
Speaking of Armstrong's computer, the police said "no data is to be recovered," without further explanation is to why they could not or would not recover the data.
What is the explanation is that there is no data from that dive on the computer? What if the computer, too, was "bone dry"?