I would agree that capital punishment of any kind is an improvement upon no capital punishment, in that it avoids prison overcrowding in a small extent, and also that it removes the criminals.

In the present form you’re advocating, the reformation system is basically trading a reformed criminal for an innocent civilian, which is hardly a fair trade, considering one has transgressed severely and is getting off for it, while the civilian has done nothing warranting punishment, but yet dies.

The only real way you can improve the system is either improve the law system to the point that innocent people aren’t condemned to death, or figure out a way to prevent the reformees from having the ability to kill again.