How have conspiracy principles been interpreted in criminal cases?

"Conspiracy principles are often properly utilized in cases wherein the crime of conspiracy is not charged in the indictment or information. In some cases, for example, resort is had to such principles in order to render admissible against one defendant the statements of another defendant. [Citations.] In others evidence of conspiracy is relevant to show identity through the existence of a common plan or design. [Citation.] In still others the prosecution properly seeks to show through the existence of conspiracy that a defendant who was not the direct perpetrator of the criminal offense charged aided and abetted in its commission. [Citations.]" (People v. Durham (1969) 70 Cal.2d 171, 180-181, fn. 7.)