If someone breaks into your home, harms your family (think of Death Wish), but you manage to subdue him and...

...tie him up or whatever. Can you torture (exact the same amount of inflict bodily harm) towards that criminal that he used on you and your family? Once you have an offender under control, can you by law still kill that person and still call it self defense? Or are there laws that prevent you from doing this... like a small scale version of the Geneva Convention?