MBE Trap: Conspiracy

x and y agree to rob a bank, and both take all necessary steps to prepare to commit that crime. Y not only changes his mind and decides not to rob the bank, but he explains to x with full clarity that he wants nothing do do with the robbery and he calls the police so that the police are waiting for x when x arrives to rob the bank. X is arrested and would not have been arrested at that time had y not tipped off the police.

The main point: no matter what facts the writers give you about everything y did to thwart the crime, and the certainty with which y explained to x that y wanted nothing to do with the crime, y has not withdrawn from the conspiracy to commit bank robbery.

Here's why: you can only withdraw from a crime before it's been committed. It makes no sense at all to claim that someone can withdraw from a crime that has already been committed and the crime of conspiracy is simply an agreement to commit another crime (along with an act that evidences that agreement). That crime was complete before y decided that robbing banks was not for him.

What y did likely do is withdraw from the bank robbery. That crime does not merge with the crime of conspiracy, so be careful not to think that withdrawal from one is withdrawal from all.