MBE Trap: Conspiracy

Imagine 2 people (call them x and y) agree to commit bank robbery (inflation, and all that), and each performs an act sufficient to evidence that they had that agreement.

X decides soon after not only to inform y that he wants nothing to do with the bank robbery, but also to take an additional step of informing the police of y's plans so that the police are waiting for y at the bank. The police are in fact waiting for y and arrest him before any robbery takes place. X has *not withdrawn from the conspiracy. The trap in these questions is that x has withdrawn from something, but he's withdrawn from the crime that was the subject of the conspiracy (the bank robbery). Once a crime has been completed, there's no withdrawal, and the crime of conspiracy was completed upon the agreement and the act evidencing the agreement. If you want to withdraw from a crime, you're going to need to do that before you've completed the crime. To avoid falling for this trap, it should be enough to remember there's no withdrawing from the crime of conspiracy (once the conspiracy has occurred), but it is possible (as was done here) to withdraw from the crime that was the subject of the conspiracy if sufficient steps are taken to effect that withdrawal.