In the UK and US, for some very serious crimes (and this would qualify), the perpetrators are tried as adults. In UK, from what I remember, the sensational cases of Mary Bell (a ten year old girl, the youngest murderer in modern British history), and the killers of Jamie Bugler (Thompson and Venables) prompted a large outcry, and I think those are what led to juveniles between 10 and 17 to be tried as adults in future. (Not retroactively, of course.)
The idea behind juvenile courts and justice systems is that youngsters may not always be able to judge right from wrong, legal from illegal, and so on. But for horrific crimes like these, there is nobody above the age of ten who doesn't know the gravity of the act. There is no reason to let a 17.5 year old (or a 11 year old) walk away with a mere rap on the knuckles (two years in a juvenile detention center), after he raped, brutalized, impaled and murdered a fellow human being.