Without all of the facts being detailed, my sense of this guy is he is not someone who has been abused by anyone. He was raised with a sense of entitlement and power. His father may lack moral values and if so could have transmitted this absence to his son. If he is an only child or oldest, he was indulged by both his parents. He most likely has not achieved anything, because he has been granted rewards without effort. Most likely, his mother is nurturing and indulging but is ruled by both he and his father
He needed accomplices to his criminal behavior as a way to pass blame for his actions should the need arise (an insurance policy and fans). Also, he likes to influence others and to have them participate and give him recognition. He lacks empathy and others are there for his use.
It is likely, this victim presented resistance he did not usually encounter and he reacted with anger and impulsivity probably enhanced by alcohol and fueled by rejection. It is unlikely he intended to kill her. (see Current Affairs)
some more comments
This kind of assessment is difficult since we can not evaluate a crime scene or obtain evidence from a body. We have to utilize what we have without knowing so much that it complicates perception.
That said, I will do it anyway.
This crime does not seem to have been premeditated or planned in advance. At least not the murder. Although it is possible he has murdered before, I do not think so. He could have had experience and known how to dispose of the body and the scene, but it is a small island, and easy to drop a body off of the rocky side even without planning. It is unlikely he put the body where it could be found. He knows the island very well, and would not have had to think that part out ahead of time. Had there been a pattern of disappearances, it would likely have been noticed and investigated. My sense is he has ignored the rights of women, he is sensitive to rejection, and is impulsive. Most likely, the situation escalated until he felt a loss of power over the situation and he reacted aggressively.
I notice he as a strong well-proportioned physique based on the short clip I saw of him walking. He stands straight and walks with what appears to be a confidence in his strength. He is uniformly developed in his upper and lower body. He appears to have a sense of power in his physical strength.
I was interested in his refusal to accompany police when requested. He did not seem to initially recognize their authority over him or to fear resistance. He seems to have withstood interrogation well, over an extended period of time in spite of his youth. This indicates to me a certain confidence that he will not be held accountable for his actions.
I also think if this had been organized, and well planned, he would have made sure he was not seen with her on the night of the murder. It is more likely it was unplanned, an escalation of behaviors he had committed in the past, and that he had some assistance from his father, or someone in the cover-up.