Section 565.020 - First degree murder, penalty - person under eighteen years of age, penalty1. A person commits the offense of murder in the first degree if he or she knowingly causes the death of another person after deliberation upon the matter.2. The offense of murder in the first degree is a class A felony, and, if a person is eighteen years of age or older at the time of the offense, the punishment shall be either death or imprisonment for life without eligibility for probation or parole, or release except by act of the governor. If a person has not reached his or her eighteenth birthday at the time of the commission of the offense, the punishment shall be as provided under section 565.033.Amended by 2016 Mo. Laws, SB 590,s A, eff. 8/28/2016.L. 1983 S.B. 276, A.L. 1984 S.B. 448 § A, A.L. 1990 H.B. 974