My guess is strangulation, because it fits that narcissistic psychopath boyfriend. It is the ultimate power play, and so easily done to a slight young girl like Gabby.
That sounds similar to a case in a town where I lived. In an argument with his girlfriend, the young man (who everyone thought was a nice guy), also in his early 20’s, snapped and grabbed his girlfriend’s neck. Then he tried to cover up the crime by dumping her body somewhere. That woman was small and slight, too, and later, of course, he claimed she died quickly and he didn’t mean to kill her.
My thinking too. Laundrie was a narcissistic psychopath who showed his colors when he was observed slapping and shoving Gabby:
Caller: “Hello, uh, I’m calling. I’m on the corner of the main street near Moonflower and I’m driving by. I’d like to report on a domestic conflict. Florida – with a white van – Florida license plate, white van, gentleman about 5-6 … “
Coordinator: “Where are you?”
Caller: “They just ran away. They went down the main street. They turned right from Moonflower to the main street … Cooperative.”
Coordinator: “And what were they doing?”
Caller: “What did you say?”
Coordinator: “What were they doing?”
Caller: “We passed by, and the gentleman was slapping the girl.”
Coordinator: “Did he slap her?”
Caller: “Yes, then stopped. He ran up and down the sidewalk. He started hitting her, jumped into the car, and they ran away.”
Coordinator: “Okay. Did you say it’s a white van?”
Caller: “White van. I’ll give you a license plate in a second. I took a picture.”
Coordinator: “Well, what kind of white van? Like a big one?”
Caller: “Hmm, it was a small van with the Florida license plate QFTGO3 license plate. It was white. It was a manufacturer and a Ford model with transit. A black ladder on the passenger side. “
Coordinator: “Black ladder, passenger side?”
Caller: “White Ford Transit.”
Coordinator: “White Ford Transit … Well, what’s your name?”
Coordinator: “And where were they? So did they turn around and head south on Main Street from Moonflower Market?”
Caller: “Correct. They turned right.”
All it would take would be for Gabby to cut him off from sex as her way to control him. That would set off a chain reaction resulting in a grab to her neck.