Which of the following is NOT a mitigating factor for 2nd degree murder?

Killing in self-defense is generally not considered a mitigating factor for second-degree murder. Instead, it is recognized as a complete defense that can result in a verdict of not guilty. In cases of self-defense, the individual argues that they had a reasonable belief that they were in imminent danger of death or great bodily harm, leading them to take lethal action. Therefore, if a person can demonstrate that their actions were purely defensive and justified under the circumstances, they would not be charged with murder at all, let alone second-degree murder.

In contrast, the other options—serious provocation sufficient to excite a reasonable person and acting under sudden and intense passion due to provocation—are indeed mitigating factors. They can reduce a murder charge from first-degree to second-degree because they indicate that the individual was not acting with premeditation or the intent to kill in a planned manner, but rather was driven by emotional reactions to provoking behavior.