(1) A person commits the offense of negligent homicide in the first degree if that person causes the death of:
(a) Another person by the operation of a vehicle in a negligent manner while under the influence of drugs or alcohol; or
(b) A vulnerable user by the operation of a vehicle in a negligent manner.
(2) A person who violates subsection (1)(a) shall be guilty of a class B felony; provided that the person shall be guilty of a class A felony when the person:
(a) Has been convicted one or more times for the offense of operating a vehicle under the influence within fifteen years of the instant offense;
(b) Is, at the time of the instant offense, engaging in conduct that would constitute a violation of section 291E-62; or
(c) Is a highly intoxicated driver as defined by section 291E-1.
(3) A person who violates subsection (1)(b) shall be guilty of a class B felony.
(4) Notwithstanding sections 706-620(2), 706-640, 706-641, 706-659, and any other law to the contrary, the sentencing court may impose a lesser sentence for a person convicted of a class A felony under this section if the court finds that strong mitigating circumstances warrant the action. Strong mitigating circumstances shall include but not be limited to the provisions of section 706-621. The court shall provide a written opinion stating its reasons for imposing the lesser sentence.
(5) For the purposes of this section, a person "has been convicted one or more times for the offense of operating a vehicle under the influence" if the person has one or more:
(a) Convictions under section 291E-4(a), 291E-61, 291E-61.5, or 291E-64;
(b) Convictions in any other state or federal jurisdiction for an offense that is comparable to operating or being in physical control of a vehicle while having either an unlawful alcohol concentration or an unlawful drug content in the blood or urine or while under the influence of an intoxicant or habitually operating a vehicle under the influence of an intoxicant; or
(c) Adjudications of a minor for a law violation that, if committed by an adult, would constitute a violation of section 291E-4(a), 291E-61, or 291E-61.5,
that, at the time of the instant offense, had not been expunged by pardon, reversed, or set aside. All convictions that have been expunged by pardon, reversed, or set aside before the instant offense shall not be deemed prior convictions for the purposes of this section.