As always, everyone gets seriously heated about this issue, and mutters about 'death is too good for them, I'd pull the lever ...' and similar.
As I mentioned on another thread, emotion and the law do not go together, because that way is anarchy and vigilante hell.
An appropriate sentence should be issued and served, and if at the end of that, these people need protection by false identities, it should be offered - regardless of some eight-figure cost dreamed up by the media who fan the flames of everyone's righteous anger.
Revenge is not a legal process, it's the 'strongest' meting out their own 'justice' and it simply has no place in a civilsed society.