When you read something describing in detail a person's intent to do something very bad, in a place where they write things that they intend to do, and which in the past they have in fact consistently done, you don't attach any significance to that at all?
I certainly think a police officer that stumbled across such a thing would be justified in asking follow-up questions like 'hey, what's this about you going to shoot someone?' and then maybe making an arrest based on your replies/demeanor.
'Probable cause' should involve a degree of certainty, because 'possible cause' would be altogether too loose of a standard. It's possible that you're intending to shootme and you just mentioned saulpw to throw other HN users off the scent. Possibilities are only limited by the assessor's imagination.
Suppose you go further: You write the "story", and "agree" with a friend to carry it out. Then you go to a gun store and buy a gun ("overt act").
How can I prove that all this is not just a dark and morbid roleplay?
And yet US federal law will convict you for conspiracy to commit murder on this evidence, as I understand it.
If you think the "dark and morbid story" defence is reason enough not to make writing the threat down a crime, why do you think the "dark and morbid roleplay" defence is unsound?
How does the cop at the traffic stop know that your username is akoboldfrying? Did you tell them? If so, why, at a traffic stop, did you do that?
Are you posting threats on hacker news while you are driving? And the cop was close enough to see your username and what you wrote? Is that why you were pulled over?
I don't see how any of these questions are relevant to the point I'm making.
Do you dispute that people sometimes discover things about other people? Do you dispute that things a person discovers about another person can change the first person's assessment of what the second person might do next?
Because it seems to me that you are merely picking apart concrete details of an example situation that are not relevant to the general issue that the example is clearly trying to demonstrate.
I was reaching for a scenario that concisely demonstrated the core aspects of the general issue; maybe the example I chose wasn't very good. The core aspects are what are important, though. They are:
1. Someone in authority can discover recorded information, one interpretation of which is that that someone else is plotting a crime
2. The information might not have been subject to any agreement with (or even seen by) a second person
3. Should that discovery be taken seriously enough to warrant arresting the person?
My claim is that yes it should, unless there are other clearly overriding factors.
