IMHO, there was no hired gun. I base my opinion on prior cases such as Scott/Laci Peterson, Josh/Susan Powell, Mark/Lori Hacking. The typical sociopathic murderer acts alone, again, IMHO.
I believe he planned it out ahead of time. Here's one possible scenario, not my only one. He parked his truck in a hidden, but safe-ish location not far from where he planned to abandon her SUV. Called Charli. When she arrived, he offered her some drugged food and/or a beverage. For the sake of discussion, a bottle of orange juice. The drug would not have to be anything out of the ordinary, just something that would make her very sleepy - a couple of Benadryl would do it for me. Then he tells her, let's go, I'll drive, gets in the SUV with Charli, Nala, and the orange juice and drives off. They drive up Hana Hwy. until Charli falls asleep, somewhere near Nahiku. He opens up the SUV and lets Nala out. Drives back to where he has planned to dispose of the body. I'm thinking it's along Nua`ailua Bay, close to the shore. At this point, Charli is alive, but nearly unconscious from the drug. He drags her out of the vehicle, removes her clothing and kills her - the roaring surf would mask the sound of a gunshot. Clothing was removed so it would not be bloody. Then he either disposes of the body in the surf, or digs a shallow trench in the soft mud, rolls the body in the mud, and buries it. He takes the clothing to a different location, not too far away, and abandons it as though someone went for a swim. Then he drives back to where Charli's SUV was abandoned, somewhere where he was nearly certain that the "wrecking crew" boys would find it, strip it, and drive it to the Peahi Rd. area and torch it. Then he walked back to his truck and drove home.
I am thinking that he drugged her so that she would not fight back. If she'd fought back, he would have to explain scratches and bruises.
