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?
Yep he tried to kill her one way (bashing her head, maybe pushing her down and causing her to hit her head).... and when she didn't die he strangled her. Everything he did after that was some bullshirt attempt to make it seem like it wasn't in cold blood or that he didn't do it. Sorry, doesn't add up, not even a little. He killed her in cold blood and his family helped him try to cover his tracks and spin the story.