Can the defendant be charged with conspiracy, murder or car theft after wanting out of the plan?see People v. Sconce 279 Cal. Rptr. 59 (Call. App. 1991)
The short answer is yes. In the case you cited there is a lengthy explanation regarding the differences in the charges and why the case was handled in a particular way.
A conspiracy is a separate act whether or not it results in a crime. The crime itself is typically prosecuted separately, or at least is charged differently. For example: You and a friend conspire to create and execute a major black mail scheme. Just before the scheme occurs your conscience gets the better of you and you back out. The friend commits the crime. While you cannot be charged with the crime itself, you are still responsible for the conspiracy. Other crimes may also have individual charges such as accessory before and after the fact, depending on the case.
The case you speak of: People v. Sconce 279 Cal. Rptr. 59 (Call. App. 1991) was prosecuted under California law. You must also take into consideration that some states will prosecute cases in different ways pursuant to the state law.
To drive the point home: Charles Manson was never convicted of murder since there was no proof he had ever killed anyone. He was charged and convicted on conspiracy charges.