Here are some possible scenarios.
1. He was killed in some freak accident where one of his friends was driving drunk. Now, I appreciate the thoughtfulness of those who have wondered about this. I understand that police wanted to know about a vehicle. But, if you think about, how likely is it that someone who was not driving a car when a friend was killed is going to agree with the driver that they really should toss the body into the ocean and play dumb or, heaven forbid, dismember him. I do not think it would be this scenario.
2. He was killed by his fellow campers for something that he had done or said or was going to do or say. In this situation, perhaps they had it in for him and invited him to go camping with the plan to murder him. I see this as more likely. For example, he narced out some soldiers or cheated with another soldier's girlfriend or wife. If it was relationship related, then I doubt that a group would be involved. But he could have done something to the whole group.
3. He was killed by someone he didn't know. This is the one I think is most likely. He may have gone for a walk at night. Possibly, he could have decided to go to a bath house. In this scenario, a lot of the stuff where it seems that his friends were not being truthful is probably just misunderstandings in terms of what they said and did and what got reported.