Not QUITE the situation you're describing here but there was a chronically pissed-off Russian dude with a foul attitude who was being let go one Friday and I shared an office with him. I was warned ahead of time that he was out the door in case anything weird or surprising happened.
Anyway, around 4 PM I went to go talk to my boss about something and do some whiteboarding. When I came back, I collected my laptop and went home for the weekend.
About 7 AM the next morning I wake up to my boss blowing up my phone which was in itself an odd thing.
He asks me if I have my machine with me, which I do. "Now I trust you and know you're not stupid enough to do something like this and besides, I know where you were around 4 PM but could you check your mail and look at your outbox?"
Sure enough, there was a no-punctuation email from my outbox around that time sent to a certain CEO of this company who might have been known for being loud, sweaty, bald, and having a bit of a temper. He's no longer CEO either if you're trying to guess who I'm talking about.
Anyway the email just read "fuck you much" and was reply-forwarded to about four levels of management including my boss with the words "excuse me?"
That's right, I was a dumbass who didn't lock my machine when Crazy Russian got shitcanned, and I guess he didn't like me too much either.
Anyway, after we quickly figured out what was going on we decided the best course of action was to send an apology where I truthfully explained I hadn't locked my machine and would be more mindful of security policy in the future, very sorry, etc etc.
Whoever monitors the CEO's email responded back fifteen minutes later with "no sweat."
That's it. Open and shut case.