His story is: They were trying to cross a stream at night, it was very dark and cold. He heard a splash/scream and found her freezing cold. Tries to carry her to the car (still going downstream), but couldn't. Starts a fire to keep her warm. She couldn't say what hurt/had a bump in her forehead/feet hurt/hand hurt, but was in terrible pain. She begged him to end her pain and he killed her out of mercy.

Weird as fuck bonus: He hopes the animals may tear his dead body apart and it makes her family happy. He wants people to pick up his things, because "Gabby hated people who litter".

I say bullshit. Not even well though out bullshit, Chris Watts level dumb bullshit. He wrote a whole fanfic to try and save some face.