Ah well....
The idea appeals to me but that is just one opinion and the right or wrong of it is always debatable.
The only thing that seems certain to me is that the actions of private individuals in this specific type situation will not have an iota of influence on future captors. I just doubt their decisions regarding the life or death of captives are based on fear of reprisal.
Remember, the death penalty is not a deterent to murder nor can it be proven that the fear of dp is anything more than a convenient excuse to indulge in the murder of potential witnesses.