About 10 minutes into the dive John turned to look at Jennifer, who had been swimming slightly behind him, and realized that she was not there. Turning to look for her, he saw someone in the dimness ahead and swam in that direction. As he approached, he saw that it was Jennifer. John realized she was unconscious, but doesnt recall whether or not she had her regulator in her mouth. Grabbing her by her BCD, he attempted swimming to the surface. John was kicking hard, but not making any progress toward the surface. He didnt think to release her weights or inflate her BCD, and in a very short time the exertion was taking a toll.
When reading stories like those out of Diver Down, it's good to read between the lines and explore the multiple failings that got those divers in to trouble. Most of those failings are initially from the victim such as in this case. Jennifer didn't establish anything close to neutral buoyancy at depth, resulting in John being unable to swim her up. John was also probably negative during this scenario and/or showing very poor finning technique.
We don't know the reasons for Jennifer losing consciousness however one could surmise that being negative and kicking to maintain a certain depth increased her breathing to a shallow spiral of CO2 rich inhalations. She didn't 'Stop, hold on to something (where feasible), catch her breath, and then move on at a slower pace' which again is taught during the 'typical' OW course.
Nor do we know the time frame between learning to dive and the final accident. Was Jennifer trained last week? Last year? Was she a regular diver or, like many people, an irregular diver who hadn't dived for 6 months, and decided not to take a refresher course, which is designed especially for this common scenario.
Releasing weightbelts is also covered in typical OW courses. SSI actually conducts weightbelt removal underwater. PADI has decided not to make it a practical exercise- perhaps deeming it too risky for OW students. There are multiple references to removing weights in 'typical' OW courses no matter what the agency.
IMO there comes a time for divers to make the realisation that diving is an inherently dangerous hobby. Some instructors do not stress this point enough, however PADI does talk about the risks of diving, asks for a fairly comprehensive medical statement, asks for various liability releases etc. before even getting your toes wet. Individuals need to understand that learning to dive is one thing, however 'being a diver' is something that requires dedication of time, money and effort- and nobody can do it for them.