As much as we may believe that we, as humans, can inflict pain and suffering on these criminals, death will always remain the best option for them. Let Allah SWT deal with them; the punishment of the grave is more severe than anything we could ever hope to achieve.

‏سُبْحانَ الله وَالحَمْدُ لله وَلا إِلهَ إِلاّ الله وَاللهُ أَكْبَرُ