Unfortunately there are some people who have a nasty streak in them, who will do unspeakable things. In this case, it manifested very early in life, but this may be something that will happen more and more, because kids are subjected to a barrage of violent behaviour through the media (who glamorise and portray it from the wrong angles from time to time), through video games that glamorise violence, to the internet where they freely say whatever they want and are subject to nowhere near the same rules as in 'real' life.
The kids nowadays see violence as something that is commonplace, they seem to actually like it. It is encouraged in some ways, and they are starved of any discipline that could control them in the way a certain percentage need. They are also living in an age where they are scarcely tolerated, hounded away from built-up areas, and left to their own devices. They are frowned upon by the majority of adults and told they are useless, stupid and starved of encouragement for initiative.
Unfortunately, the kind of person who is capable of the cold-blooded and meaningless extreme violence, is not the rehabilitating kind in my experience, and they tend to need to be kept off the streets as long as possible. In this case, these two perpetrators are more than likely a lost cause, will be nothing but a wasted life, and will grow up and be educated in the prison system. The only way to make them of any use is to punish them like we never have before, to show them as an example to other kids, and scare some out of acting on their under-developed thoughts.
Its a fact of life now, and until we as a country start to punish people rather than try to understand them all the time..... we're gonna have to get used to reading about it.