And when there isn’t a specific law, there is a general “conspiracy to commit” law ( https://en.wikipedia.org/wiki/Criminal_conspiracy ), which is what I’m sure is involved in this case.
“Conspiracy” makes it sound funny, but the basic idea is that when multiple people (and “multiple” means “at least two”) have conversations about committing a specific crime and one takes concrete steps toward committing that crime, then all people involved can be punished for conspiracy. Of course, the ones who were undercover agents don’t get punished. And the fact that the plan wouldn’t work doesn’t matter. If the FBI sells fake explosives to somebody and that person plants them outside a building and tries to set them off, the fact that they were fake doesn’t help them beat the rap.
The issue with stalking is that there isn’t a law against being in the same area as somebody else (unless there’s a restraining order). So, unfortunately, the police can’t make an arrest until a law is broken or the potential stalker at least tries to break the law.
They're probably still committing a crime. The thing with terrorism vs stalking though, is the budgets that are being spent on preventing them. It's also the level of Law Enforcement that does the investigation. Local PD is much less capable and has much less man power than the FBI.
Also, in case of 'tells a victim of planned murder plots' this often happens in person with no record existing. This happens about as often as fake victims saying someone is threatening them. So it's hard to judge whether any report of death threats from a stalker is real.
I've personally worked on stalking cases and until you've got actual irrefutable evidence of a stalker having made threats, it's always a gamble. Even letters and messages are being faked by pretend victims. Overreaction by local PD, without evidence, is how people get shot when they get swatted.
https://theintercept.com/2015/03/16/howthefbicreatedaterrori...
You might be interested in the "cannibal cop" case.
https://en.wikipedia.org/wiki/United_States_v._Valle
Where, exactly, is the line crossed between "this guy is talking shit" and "this guy is actively planning to do harm?"
(I don't know where I even stand on that case. The ramifications of every alternate outcome is equally unsettling.)