It's hard to form an opinion without knowing what is "this thing" the author has done, unless I missed the part where he describes it. If he acknowledged to a colleague of having killed someone, the context is pretty different from a minor violation of an internal policy.
From some of my experiences with corporate HR departments, it can be impossible to tell exactly what happened even when you are the one who is supposed to be in the wrong. This is another reminder that Human Resources is there to protect your company from you, not protect you from your company.
This. Unions might be helpful here depending on how they work in your country, but this story is so vague that I got the feeling that HR actually did their part. Sure sucks to loose your job, but if you are given restraints and disregard them, well what do you expect to happen?