What is the corpus delicti rule in the context of a criminal case?

The corpus delicti rule provides that " '[i]n every criminal trial, the prosecution must prove the corpus delicti, or the body of the crime itselfi.e., the fact of the injury, loss, or harm, and the existence of a criminal *406 agency as its cause. In California, it has traditionally been held, the prosecution cannot satisfy this burden by relying exclusively upon the extrajudicial statements, confessions, or admissions of the defendants. [Citations.]' [Citation.] This includes 'preoffense statements of later intent as well as ... postoffense admissions and confessions.' " ( People v. Miranda (2008) 161 Cal.App.4th 98, 107, 73 Cal.Rptr.3d 759.)