Like it or not, justice is supposed to be blind (hence the blindfold). While I agree that sociopathy/psychopathy can perhaps be recognized at an early age, it often cannot be definitively diagnosed before age 18. Further, not all sociopaths go on to be rapists and murderers, much less commit such grievous acts as these two did. While I agree that the likelihood of recidivism by either or both of these two is quite high, what separates our societies from those like Nazi Germany and Stalinist Russia is the rule of law that prevails, not the rule of man, at least most of the time. Most of our societies hold that children under a certain age are not held accountable
into adulthood for their acts as children up to a certain age. In the US that age varies by state, but is as low as 13, if not lower in some states. One of the side effects of such laws is that people who commit heinous acts under that age are allowed back into society at some given point in time.
In most, if not all US states these two would not only have been released by their 21st birthdays, their juvenile records would be sealed and not even be accessible to law enforcement organizations going forward. At least Britain has them on a relatively short leash insofar as they can be incarcerated at any time for a substantial period of time without trial should they find themselves on the wrong side of the law.