Life imprisonment is the greater punishment if the killer is denied
any parole and must live in a penitent state for the remainder of
his/her life.

Death is too often for killers "a consumation devoutly to be wished" and it doesn't impress upon the killer the heaviness of the deed.
Life imprisonment with no frills and the possibility of a kind of
psychological redemption without a reward other than that of itself
seems to be the best deterrent to me.

Frank