In His Book of Laws, Baha'u'llah has given death as the penalty for murder but He has permitted life imprisonment as an alternative. Both practices would be in accordance with His Laws.
According to my beliefs, if a murderer gets the death penalty God will not impose a second penalty upon the person after that person dies, but if a murderer gets life in prison God will impose a second penalty upon that person in the afterlife. So who is really better off? I guess that would all depend upon the punishment God imposes, but I for one would not want to be on the other side of God's wrath, especially given the heinous crimes I have seen people commit.
Also, according to my beliefs, if an innocent person is falsely condemned to die, God will compensate that person a thousandfold in the afterlife for this human injustice.