Will and trust undue influence cases are most often established through indirect evidence.  The following are some of the important California Evidence Code sections that pertain to the admissibility of evidence in undue influence cases . . .

GENERALLY

412.  If weaker and less satisfactory evidence is offered when it was within the power of the party to produce stronger and more satisfactory evidence, the evidence offered should be viewed with distrust.

413.  In determining what inferences to draw from the evidence or facts in the case against a party, the trier of fact may consider, among other things, the party’s failure to explain or to deny by his testimony such evidence or facts in the case against him, or his willful suppression of evidence relating thereto, if such be the case.

780.  Except as otherwise provided by statute, the court or jury may consider in determining the credibility of a witness any matter that has any tendency in reason to prove or disprove the truthfulness of his testimony at the hearing, including but not limited to any of the following:

(a) His demeanor while testifying and the manner in which he testifies.

(b) The character of his testimony.

(c) The extent of his capacity to perceive, to recollect, or to communicate any matter about which he testifies.

(d) The extent of his opportunity to perceive any matter about which he testifies.

(e) His character for honesty or veracity or their opposites.

(f) The existence or nonexistence of a bias, interest, or other motive.

(g) A statement previously made by him that is consistent with his testimony at the hearing.

(h) A statement made by him that is inconsistent with any part of his testimony at the hearing.

(i) The existence or nonexistence of any fact testified to by him.

(j) His attitude toward the action in which he testifies or toward the giving of testimony.

(k) His admission of untruthfulness.

1100.  Except as otherwise provided by statute, any otherwise admissible evidence (including evidence in the form of an opinion, evidence of reputation, and evidence of specific instances of such person’s conduct) is admissible to prove a person’s character or a trait of his character.

1101.  (a) Except as provided in this section and in Sections 1102, 1103, 1108, and 1109, evidence of a person’s character or a trait of his or her character (whether in the form of an opinion, evidence of reputation, or evidence of specific instances of his or her conduct) is inadmissible when offered to prove his or her conduct on a specified occasion.

(b) Nothing in this section prohibits the admission of evidence that a person committed a crime, civil wrong, or other act when relevant to prove some fact (such as motive, opportunity, intent, preparation, plan, knowledge, identity, absence of mistake or accident, or whether a defendant in a prosecution for an unlawful sexual act or attempted unlawful sexual act did not reasonably and in good faith believe that the victim consented) other than his or her disposition to commit such an act.

(c) Nothing in this section affects the admissibility of evidence offered to support or attack the credibility of a witness.

1104.  Except as provided in Sections 1102 and 1103, evidence of a trait of a person’s character with respect to care or skill is inadmissible to prove the quality of his conduct on a specified occasion.

1105.  Any otherwise admissible evidence of habit or custom is admissible to prove conduct on a specified occasion in conformity with the habit or custom.

EXCEPTIONS TO THE HEARSAY RULE

Confessions and Admissions

1220.  Evidence of a statement is not made inadmissible by the hearsay rule when offered against the declarant in an action to which he is a party in either his individual or representative capacity, regardless of whether the statement was made in his individual or representative capacity.

1221.  Evidence of a statement offered against a party is not made inadmissible by the hearsay rule if the statement is one of which the party, with knowledge of the content thereof, has by words or other conduct manifested his adoption or his belief in its truth.

1222.  Evidence of a statement offered against a party is not made inadmissible by the hearsay rule if:

(a) The statement was made by a person authorized by the party to make a statement or statements for him concerning the subject matter of the statement; and

(b) The evidence is offered either after admission of evidence sufficient to sustain a finding of such authority or, in the court’s discretion as to the order of proof, subject to the admission of such evidence.

1223.  Evidence of a statement offered against a party is not made inadmissible by the hearsay rule if:

(a) The statement was made by the declarant while participating in a conspiracy to commit a crime or civil wrong and in furtherance of the objective of that conspiracy;

(b) The statement was made prior to or during the time that the party was participating in that conspiracy; and

(c) The evidence is offered either after admission of evidence sufficient to sustain a finding of the facts specified in subdivisions (a) and (b) or, in the court’s discretion as to the order of proof, subject to the admission of such evidence.

1224.  When the liability obligation, or duty of a party to a civil action is based in whole or in part upon the liability, obligation, or duty of the declarant, or when the claim or right asserted by a party to a civil action is barred or diminished by a breach of duty by the declarant, evidence of a statement made by the declarant is as admissible against the party as it would be if offered against the declarant in an action involving that liability, obligation, duty, or breach of duty.

1225.  When a right, title, or interest in any property or claim asserted by a party to a civil action requires a determination that a right, title, or interest exists or existed in the declarant, evidence of a statement made by the declarant during the time the party now claims the declarant was the holder of the right, title, or interest is as admissible against the party as it would be if offered against the declarant in an action involving that right, title, or interest.

1227.  Evidence of a statement by the deceased is not made inadmissible by the hearsay rule if offered against the plaintiff in an action for wrongful death brought under Section 377 of the Code of Civil Procedure.

Declarations Against Interest

1230.  Evidence of a statement by a declarant having sufficient knowledge of the subject is not made inadmissible by the hearsay rule if the declarant is unavailable as a witness and the statement, when made, was so far contrary to the declarant’s pecuniary or proprietary interest, or so far subjected him to the risk of civil or criminal liability, or so far tended to render invalid a claim by him against another, or created such a risk of making him an object of hatred, ridicule, or social disgrace in the community, that a reasonable man in his position would not have made the statement unless he believed it to be true.

Statements Relating to Wills and to Claims Against Estates

1260.  (a) Except as provided in subdivision (b), evidence of any of the following statements made by a declarant who is unavailable as a witness is not made inadmissible by the hearsay rule:

(1) That the declarant has or has not made a will or established or amended a revocable trust.

(2) That the declarant has or has not revoked his or her will, revocable trust, or an amendment to a revocable trust.

(3) That identifies the declarant’s will, revocable trust, or an amendment to a revocable trust.

(b) Evidence of a statement is inadmissible under this section if the statement was made under circumstances that indicate its lack of trustworthiness.

1261.  (a) Evidence of a statement is not made inadmissible by the hearsay rule when offered in an action upon a claim or demand against the estate of the declarant if the statement was made upon the personal knowledge of the declarant at a time when the matter had been recently perceived by him and while his recollection was clear.

(b) Evidence of a statement is inadmissible under this section if the statement was made under circumstances such as to indicate its lack of trustworthiness.