Young couple goes on van tour of US, boy comes back with van - no girl

I think the autopsy does line up with Brian's story, but the story seems to be missing a few bits, such as how did Gabby get injured in the first place?

She didn't appear in any videos in any kind of pain, possibly some psychological issues, but not intense pain like the note describes.

The autopsy mentioned a blunt force trauma injury on the head of Gabby. Did Brian get tired of Gabby's nagging, hitting, and camp ground smell? Did she fall during a hike, than Brian freaked out? That latter question seems unlikely, but still possible. Even so, the letter seems to indicate Brian ended her life. So, however her head was injured, her life was ended with connection of Laundrie, well, at least that's what the suicide note is implying.

I believe the autopsy indicated strangulation and a blunt force trauma injury to the head, but she died of being strangled. If Brian did hit her head, what object was used? A water bottle, a bat, a rock?