2. Hacking the servers after being fired and deleting the data
3. Insulting the guy from the marketing/sales/customer service department for lack of technical knowledge.
4. Asking the woman from the customer service department to be a cheerleader to up his motivation while he fixed the customer's problem.
That's as much a management issue as a developer one. There's no way the developer should have had sole power in the first place.
I mean, I get it. In a previous life I was "the IT guy" with absolute control over my domain. But I'd have hoped most organisations would have wised up nowadays.
If true, that is a pretty easy prosecutable criminal offense. Did you press charges?
May I ask what happened with this?
For many companies step one would be to contact the feds, and then the former employee would awaken to the sound of their door being kicked in pursuant to a search warrant for all of their personal devices.
Anything related to damaging computer systems via way of unauthorized (or even sometimes even authorized) access can easily become a federal crime.
The CFAA[0] comes to mind, see 18 U.S.C. § 1030(a)(5)(A).
Moreover, the feds are typically better equipped than local jurisdictions to handle computer-related crimes.
[0] https://www.law.cornell.edu/uscode/text/18/1030
Note: IANAL