I did a google search for Peru Newspapers, I found this, it sounds like the Peruvian police do not think his confession was "sincere".
http://translate.google.com/transla...a/seccion.php?txtSecci_id=4&txtNota_id=368851
snipped from above:
Officers found several aggravating circumstances in the investigation against Van der Sloot and established that he acted with malice and ferocity against their victim to cause death, to thus seize the money she won hours earlier that day at the Atlantic City casino , so it is facing an offense against property with subsequent death, said a source.
Proof of this is that he was not the victim found any valuables in your vehicle and not on the crime scene. And the heavy blows inflicted on his victim were not only to frighten or reduce it, but had every intention of killing her. The version that holds over the circumstances that to act with extreme violence is an alibi for the sole purpose of reducing the crime.