I. A person is guilty of murder in the first degree if he:
(a) Purposely causes the death of another; or
(b) Knowingly causes the death of:
(1) Another before, after, while engaged in the commission of, or while attempting to commit felonious sexual assault as defined in RSA 632-A:3;
(2) Another before, after, while engaged in the commission of, or while attempting to commit robbery or burglary while armed with a deadly weapon, the death being caused by the use of such weapon;
(3) Another in perpetrating or attempting to perpetrate arson as defined in RSA 634:1, I, II, or III;
(4) The president or president-elect or vice-president or vice-president-elect of the United States, the governor or governor-elect of New Hampshire or any state or any member or member-elect of the congress of the United States, or any candidate for such office after such candidate has been nominated at his party's primary, when such killing is motivated by knowledge of the foregoing capacity of the victim.
II. For the purpose of RSA 630:1-a, I(a), "purposely'' shall mean that the actor's conscious object is the death of another, and that his act or acts in furtherance of that object were deliberate and premeditated.
III. A person convicted of a murder in the first degree shall be sentenced to life imprisonment and shall not be eligible for parole at any time.