“I think Mary Jo told him she was pregnant with his baby and he murdered her.”
This is possible. We saw the movie today. Supposedly, he escaped from the car, but when people tried to get into the car to rescue Mary Jo (already dead), every door was locked and every window was shut. How did HE get out? Seems possible he suffocated her, locked the doors so she couldn’t escape, and pushed the car into the water.
Were automatic door locks available on cars in ‘69? If his had the old pull-up locks, then it seems she would’ve been able to pull one up, open the door, and escape. Of course, a corpse couldn’t have done that.
It is very hard to open a door under water. The pressure of the water is too resistant. That's what under-water aerobics is all about! Even above water the doors of those vintage Oldsmobiles were heavy, heavy. I used to drive one, hauling 4 little kids to and from school, camp, scouts, etc. I couldn't believe the difference when I traded the Olds for a Ford station wagon. Easy peasy, by comparison.