actually you can.
its called conspiracy to commit bank robbery.
police have nabbed a bunch of people for crimes they were planning to commit, but stopped them before they could do so
have to have knowledge and evidence, but you can
you can be arrested for planning to commit crimes when you have them caught discussing it or telling you about it.
You are wrong, reread my post.
Conspiracy (criminal) - Wikipedia
(excerpt)
In most U.S. jurisdictions, for a person to be convicted of conspiracy, not only must he or she agree to commit a crime, but at least one of the conspirators must commit an overt act (the actus reus) in furtherance of the crime.
#JudgeBagsterPresiding
Criminal conspiracy requires more than talk. It requires action, at least one step to advance the plan. That step may itself be legal.
Example, bank robbery plan incldues acquisition of firearms. Acquiring firearms, even legally, to adance the plan to rob the bank is action. It is more than talking about robbing the bank. Without the action, there is no criminal conspiracy, only talk.
People talk much of violent overthrow of the government. This is not a crime.