Under California law, a conspirator who withdraws from the conspiracy and communicates that withdrawal to the other conspirators remains liable for the conspiracy, but avoids liability for the target offense or subsequent offenses committed by the conspirators. Here, appellants presented evidence in their first-degree murder trial that they had withdrawn from the conspiracy before their coconspirators committed a robbery on the victims which resulted in a killing. The jury was instructed on felony-murder, aiding and abetting, and liability for the acts of coconspirators. The trial court refused defense counsels’ request for verdict forms including conspiracy to commit robbery. The appellate court reversed. When the prosecution relies on a conspiracy theory to establish liability for the underlying felony, conspiracy becomes a lesser included offense of felony murder and the jury must be given the option of returning a conspiracy verdict if there is substantial evidence of withdrawal from the conspiracy prior to the killing. The error went to the heart of the defense and could not be deemed harmless. It was not error for the court to have failed to instruct that the prosecution bore the burden of proving that appellants did not withdraw from the conspiracy. However, on retrial the court should supplement the instructions with one which states that appellants had the burden of raising a reasonable doubt that their participation in the conspiracy was continuing at the time of the killing.