I'm not faulting the body cam officer at all, the officer behind the door obviously had his finger on the bang switch...
Exactly! And I fault the claim by the chief that there was no negligence or carelessness. There were at least two violations of the 4 rules, which would seem to define careless and negligent.
By claiming that it was a simple accident, he has removed any awareness of why the 4 rules are so important, and removed any urgency for follow-up training. And if they aren't going to stress the 4 rules, which are meant to prevent exactly this type of thing, then maybe they need to add another thing which could have prevented this - a safety!