Mo. Rev. Stat. § 565.023: Voluntary manslaughter, penalty — under influence of sudden passion, defendant's burden to inject.

1. A person commits the offense of voluntary manslaughter if he or she:

(1) Causes the death of another person under circumstances that would constitute murder in the second degree under subdivision (1) of subsection 1 of section 565.021, except that he or she caused the death under the influence of sudden passion arising from adequate cause; or

(2) Knowingly assists another in the commission of self-murder.

2. The defendant shall have the burden of injecting the issue of influence of sudden passion arising from adequate cause under subdivision (1) of subsection 1 of this section.

3. The offense of voluntary manslaughter is a class B felony.