(a) A person is guilty of murder when, with intent to cause the death of another person, he causes the death of such person or of a third person or causes a suicide by force, duress or deception; except that in any prosecution under this subsection, it shall be an affirmative defense that the defendant committed the proscribed act or acts under the influence of extreme emotional disturbance for which there was a reasonable explanation or excuse, the reasonableness of which is to be determined from the viewpoint of a person in the defendant's situation under the circumstances as the defendant believed them to be, provided nothing contained in this subsection shall constitute a defense to a prosecution for, or preclude a conviction of, manslaughter in the first degree or any other crime.
(b) Evidence that the defendant suffered from a mental disease, mental defect or other mental abnormality is admissible, in a prosecution under subsection (a) of this section, on the question of whether the defendant acted with intent to cause the death of another person.
(c) Murder is punishable as a class A felony in accordance with subdivision (2) of section 53a-35a unless it is (1) a capital felony committed prior to April 25, 2012, by a person who was eighteen years of age or older at the time of the offense, punishable in accordance with subparagraph (A) of subdivision (1) of section 53a-35a , (2) murder with special circumstances committed on or after April 25, 2012, by a person who was eighteen years of age or older at the time of the offense, punishable as a class A felony in accordance with subparagraph (B) of subdivision (1) of section 53a-35a , or (3) murder under section 53a-54d committed by a person who was eighteen years of age or older at the time of the offense.