(1) Except as provided in subsection (2) of this section, any person convicted of the crime of aggravated first degree murder shall be sentenced to life imprisonment without possibility of release or parole. A person sentenced to life imprisonment under this section shall not have that sentence suspended, deferred, or commuted by any judicial officer and the indeterminate sentence review board or its successor may not parole such prisoner nor reduce the period of confinement in any manner whatsoever including but not limited to any sort of good-time calculation. The department of social and health services or its successor or any executive official may not permit such prisoner to participate in any sort of release or furlough program.

     (2) If, pursuant to a special sentencing proceeding held under RCW 10.95.050, the trier of fact finds that there are not sufficient mitigating circumstances to merit leniency, the sentence shall be death. In no case, however, shall a person be sentenced to death if the person was mentally retarded at the time the crime was committed, under the definition of mental retardation set forth in (a) of this subsection. A diagnosis of mental retardation shall be documented by a licensed psychiatrist or licensed psychologist designated by the court, who is an expert in the diagnosis and evaluation of mental retardation. The defense must establish mental retardation by a preponderance of the evidence and the court must make a finding as to the existence of mental retardation.

     (a) "Mentally retarded" means the individual has: (i) Significantly subaverage general intellectual functioning; (ii) existing concurrently with deficits in adaptive behavior; and (iii) both significantly subaverage general intellectual functioning and deficits in adaptive behavior were manifested during the developmental period.

     (b) "General intellectual functioning" means the results obtained by assessment with one or more of the individually administered general intelligence tests developed for the purpose of assessing intellectual functioning.

     (c) "Significantly subaverage general intellectual functioning" means intelligence quotient seventy or below.

     (d) "Adaptive behavior" means the effectiveness or degree with which individuals meet the standards of personal independence and social responsibility expected for his or her age.

     (e) "Developmental period" means the period of time between conception and the eighteenth birthday.

[1993 c 479 § 1; 1981 c 138 § 3.]