And also perhaps you are over thinking it. That's the thing with PTSD, it doesn't have to be a 'valid' reason for the outburst, or the anger. Usually, it isn't. It's a small everyday thing that the PTSD brain twists and turns into something completely different and more significant. That is really one of my points during this whole discussion, when someone has PTSD, who they are, as in what type of personality they have or had prior to getting the PTSD, has nothing to do with the PTSD reactions. PTSD can change the quietest, most reserved or the happiest most outgoing person into a paranoid, aggressive, fearful, angry person in moments of stress or perceived stress.
In this case, it could have been something as simple as he had a headache, and she yelled from her car to his about paying for the gas. Nine times out of ten, that is exactly what it sounds like, someone getting your attention and reminding you to pay for the gas. That ten time, in a PTSD mind, that is her yelling at him and saying he is a failure, incompetent and not able to take care of himself, inciting fear, aggression and anger.
PTSD is a trigger disability, that changes a person's entire personality during times of stress. The trigger often has nothing to do with the reality of a situation, but more often the perception of the person with PTSD. And yes, depending on how severe the PTSD is, they paranoid, emotional reactions can last for days. I count the days my SO is 'normal' or his old self on one hand in a month, and the days he is 'PTSD'ing' are numerous. This is what makes PTSD such a tragic disability.
It doesn't make it an excuse. Nor mean that a person should not pay for their actions while under the influence of PTSD. It just makes it more understandable when things happen. I think, if it was Howard, he lost it, attacked her, either with the knife or with his hands, and somewhere in his mind realized what he had done, panicked, tried to cover it up to make it look like a random murder, then went into total denial. What I don't know, and have no idea of knowing is at what point he began to admit to himself he did this, and began to go into the 'PTSD damage control mode'. I think it is when they found the car, but I'm not sure. At any point, the PTSD would have been telling him 'hide it, don't let anyone know you are a monster, they will hang you, they will beat you, they will lynch you' from whenever he stopped denying it to himself. It doesn't make it acceptable, it just makes it pitiful if from my point of view.
I sure hope she wasn't left in that ditch to die, I hope it was over quick for her, and the majority of wounds were not felt due to unconsciousness, hopefully, if they weren't post mortem.