I don't work in the IT department at my full time job, but I can tell you what we have in place as far as what I see at least.
1. Policies which are determined by the top management - IT, Executive...
2. Logon notice which reminds every user that the computer, etc, is company property and for company use only. You cannot logon to any computer without "agreeing" that you understand this.
3. Annual review of company policies such as data safeguarding.
4. One such policy is to always leave your machine turned on (with info stating why: so IT can push updates when/if needed).
If this person has acted this way more than once, I'd suggest that regardless of the reason, that person needs to be dealt with. In our day, people are going off the deep-end for seemingly sillier and sillier things. If nothing else, you may very well need to notify your manager, that person's manager and/or someone in HR. Whatever you do, don't get into a I said/he said type situation. If you contact the person back, it'd probably be best via a polite email, which you cc or even bcc your manager at the least.
You can nip this in the bud while still being nice and polite. If you just ignore it, and it's happened already before, well, things may very well get worse. And what's bad is that the worse part may not involve you. If he got to "run over" one person, the worse might come when he does the same with someone else... perhaps a nearby coworker.
If nothing else, do be particularly mindful of that user, and keep a close eye out for any even seemingly disturbing looks, acts, etc. Don't act suspicious or anything silly, but just be mindful that this person has already exhibited SOME signs of aggression, even if it was just via an email.
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"If to err is human, then I must be some kind of human!" -Me
