The courts were upset with the fact capital punishment would be more of a deterrent than an effective life sentence, which consists of people remaining in prison for the rest of their life or until pardoned.
Life imprisonment is any sentence of imprisonment for a crime under which convicted people are to remain in prison either for the rest of their natural lives or until pardoned, paroled or otherwise commuted to a fixed term. The state contended that while the use of capital punishment served no rehabilitating purposes, it was a legitimate punishment for retribution in serious offenses, in that it served to isolate the offender, and was a useful deterrent to crime. The court rejected the state's defense citing that there were far less onerous means of isolating the offender, and the lack of proof that capital punishment is an effective deterrent. 
