We know that auto firmly believes that he should follow the orders given to him, and that he has the taser. And I don''t think that it would be impossible that he killed a previous captain.
We also know that Auto tried to hide the fact that earth was not safe to return to from the captain. We know that once Captain McRea finds out about earth he immediately wants to go back to earth. Once Auto finds out about this he almost instinctivly tries to kill Captain McRae. Why is this his first instinct and not to explain how much it would harm them. Once you think about all this it doesn't seem too far fetched to think he may have killed a previous captain. who found out about earth not being habitable. What do you guys think about this. Please give criticism as this is my first theory.