What is the test for evidence of third party culpability in a criminal case?

For third party culpability evidence to be admissible under California law, " ' "there must be direct or circumstantial evidence linking the third person to the actual perpetration of the crime." ' " (Prince, supra, 40 Cal.4th at p. 1242, italics omitted.) Further, "the exclusion of weak and speculative evidence of third party culpability does not infringe on a defendant's constitutional rights." (People v. Gonzales (2012) 54 Cal.4th 1234, 1261.)