Touching mission critical things always has risk and those risks have to be mitigated at a political level. If the programmer is this bad at respecting political ownership of responsibility, he has no business touching production this way.
You are absolutely correct that he had no authority to perform modifications to a critical public service, and that his actions bordered on reckless and negligent and that his response to the captain's accusations was cringe-worthy as well as indicative of the ignorance of his actions, but I think it stands to reason that the captain could have handled the situation more diplomatically.
Granted, I would probably get into a shouting match with Clemans for what he did (and I'm just another developer), but that hardly justifies barring him from entering the premises until further notice.
Clemans' actions can be chalked up to youthful ignorance and exuberance, whereas the captain has no excuse. He is the central source of truth and the ultimate arbiter in the situation, he should know better than to react so aggressively to one of his own staff members.
You can't attack someone personally like that on HN—not that this would be shameful if it were true, but you clearly intend it as a slur, and that's not allowed here. Please comment civilly and substantively or not at all.
If Clemans screwed up, he had the potential to have 911 calls be routed to /dev/null. If he succeeded, the department became more efficient. However the 911 system is already working "well enough". Therefore in terms of outside perception any win will be small, and disasters could be huge.
He is not the one who has been give the authority to make this kind of risk decision. The captain is. If Clemans screwed up, the captain would be the one getting fired. Keeping the captain out of the loop is irresponsible. It doesn't matter that it worked. It doesn't matter how good the system is. You need to work with stakeholders, and not behind their backs.
However Clemans seems like the kind of person who can never understand this point.