What is the relevant evidence to disprove a defendant's intent to kill?

Nevertheless, both prior incidents were relevant to disprove facts which might have negated defendant's intent to kill. When a defendant asserts that he acted in the real or perceived need for self-defense, a prior incident may be admissible to show that the defendant did not honestly believe that deadly force was required in order to defend himself. (People v. Demetrulias (2006) 39 Cal.4th 1, 14.) Here, the prosecutor argued that the similarity of defendant's actions under similar circumstances, i.e., that any time he was faced with aggression, he pulled out a knife and went directly to deadly force, negated his claim that he held a good-faith belief in the need to defend himself with potentially deadly force. Both of the prior incidents had substantial probative value on that issue.