Selections From the Writings of `Abdu'l-Bahá
Pages 178-179
 

152: As to the question regarding the soul of a murderer, ...
 
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As to the question regarding the soul of a murderer, and what his punishment would be, the answer given was that the murderer must expiate his crime: that is, if they put the murderer to death, his death is his atonement for his crime, and following the death, God in His justice will impose no second penalty upon him, for divine justice would not allow this.