The crime of conspiracy can be charged whether or not the crime is ever actually carried out. And in some jurisdictions, no action toward carrying out the crime has to be proven for a conspiracy to exists.
For example, if two people plan to rob and bank and they go buy ski masks to wear during the robbery, they can be charged with conspiracy to commit bank robbery, even if they never actually rob the bank or even attempt to rob the bank. Buying ski masks is not a crime, but it furthers the conspiracy to commit a crime.
In most states, persons who helped plan the crime, but did not participate in the actual criminal act, can be given the same punishment as the person who carried out the crime itself. The person who commits the crime can be charged with both the crime and conspiracy to commit the crime.