c. What about the possibility of innocent people being wrongly sentenced to death?

Though the possibility of an innocent person being wrongly sentenced to death does exist, it does not make the Biblical principle of capital punishment invalid. It is the State's responsibility to ensure that an alleged killer is given as fair a trial as humanly possible and only executed if guilt is proved beyond all reasonable doubt.

Since courts are not perfect, mistakes may happen. Consolation can be taken in the knowledge that the accused will also stand before God's judgment seat where perfect justice will be dispensed on the basis of perfect knowledge. The innocent will be vindicated and the guilty condemned. On the other hand, the possibility of executing innocent persons in error is far more remote than the possibility of saving the innocent victims of criminals who may have been deterred by the prospect of capital punishment.
http://www.acdp.org.za/index.php?page=issue4