Why do kill switches when you can just hog all the work of maintaining some critical part of the infrastructure and make it's functioning and maintenance so opaque and impenetrable that the employer can't replace or fire you without their shit catching fire soon after. It doesn't have to be malicious or illegal.
His efforts to sabotage their network began that year, and by the next year, he had planted different forms of malicious code, creating "infinite loops" that deleted coworker profile files, preventing legitimate logins and causing system crashes
I wish this guy was were actually politically motivated, but he seems to have been just really petty minded person.
Does this even count as backdoor? Not really if you have to have access to the device in the first place.
https://www.youtube.com/watch?v=ndM369oJ0tk