Cal. Prob. Code § 4743

Any person who alters or forges a written advance health care directive of another, or willfully conceals or withholds personal knowledge of a revocation of an advance directive, with the intent to cause a withholding or withdrawal of health care necessary to keep the patient alive contrary to the desires of the patient, and thereby directly causes health care necessary to keep the patient alive to be withheld or withdrawn and the death of the patient thereby to be hastened, is subject to prosecution for unlawful homicide as provided in Chapter 1 (commencing with Section 187) of Title 8 of Part 1 of the Penal Code.