What?!
No, we do not follow 'eye for an eye, tooth for a tooth'-law. Bad people are bad because they do bad things, good people are good because they do good things. Easiest example: Superman and Batman. According to you, Superman would fly around and just murder all criminals.
And just for the record: these 'lowlives' never tried to kill them. *They* sneak-attacked them. Considering how shocked they reacted when their leader was killed, I doubt that they're murderer.