Who Killed the Princes in the Tower?

In 1483, the twelve-year-old King Edward V and his younger brother were put into the Tower of London by their uncle, Richard. Weeks later, Richard pronounced himself King. The boys were never seen again. For more than 500 years it has been assumed that Richard killed his nephews to obtain the crown. But is there more to this historical mystery and has Richard been grossly misrepresented?