A few thoughts ...
if he used the DVD as marker, he had it on a prior night. He's not driving around with her DVD in his truck.
If she were going to use needing gas as a pretext to leave early, she would have left before the only gas station closed, not after.
with today's computer-run pumps and registers, I think they are programmed to shut down at a fixed closing time. I've been told by various businesses they have no ability to make a sale after closing time. Especially with commodities targeted by thieves such as gas.
She didn't need a pretext like needing gas, because she had worked all day and she was pregnant and tired, reason enough to go home at 8, tend to Zoe, working in the morning.
In recent years, there's been a big push in Hawaii for disaster preparedness. We keep a full five gallon gas container that is also for the lawn tractor. Just had one of the boys borrow the gas for an empty tank on his truck a couple days ago. It's perfectly normal to have gas at hand, no stretch for Steven to have it.
I dont think Charli was planning to go anywhere, or she would have bought gas earlier. I'm just saying that if Steven needed her truck to go to Hana, most likely he could fuel it up. I think she was lured to talk about the baby somewhere in Haiku area. They maybe had a spot they had met before, considering she was not allowed at his house.
I think they went in one vehicle, and I don't think there was a vehicle left out there, because surfers go to Paraquat's and there does not appear to be anywhere to drive off the dirt road to conceal a truck. The so called road is barely drivable.
I'm on the fence about planned or unplanned. The lack of a coherent story would seem to point towards something that happened after getting in a fight. Yet there is plenty that points to him having wanted her dead for a month or so.
my idea of what could have enraged him is her telling him he is not needed to be in the kid's life and it's not his call on any decisions. I think he hated the idea of producing a child with no father because he had no father. I know he hated her family, and he did not like the idea of having to approach her family to see his baby. Remember the family commune idea ... He made several remarks in interviews that revealed resentment at being kept out of the loop, out of the decision process.
I don't think he wanted a child at all, but if it was happening, he wanted control. Control matters to this guy. Charli probably thought she was giving him what he wanted to tell him he was not needed, but I think he was furious. He's Italian after all.