“Batman”-Murderer: Difference Europe/America?

Source: Aurora, Colorado

According to the news (which can NOT generally be trusted as a reliable and well informed source) the massacre was comitted by someone who suffers from a psychiatric disorder. In Europe, this person would be convicted of the crime and then - due to the fact of the psychiatric disorder - forced to treatment and not EVER be released before a psychiatrist asserts that NO danger is to be expected any more.

In America, - at least this is the view we get here in Europe -, this person might either be executed (in a "few" years.....sometimes as many as two decades), or released as not guilty without further compulsory treatment.

I do NOT know, if this is actually the case. But from a Eurpean POV, this is what "America" (US), usually does.

Is that fair?
Is that beneficial for the community/society?