A prostitute, Alcina Dias, confirmed that [Afonso Dias] had taken Mendonça to see her on the day he disappeared. [Afonso Dias] allegedly drove up to see her in his car and asked her if she was working. When she assented, he offered to pay her to have sex with Mendonça.
and later
police forces raided alleged members of an international child pornography ring known as the Wonderland Club. The operation was code-named Operation Cathedral and resulted in the confiscation of 750,000 images and videos depicting 1,263 different children. Mendonça was among the few children (16 only) that could be identified. However, his whereabouts remain unknown and police suspect that he was murdered by his abductors after being abused on camera for other members of the paedophile ring.
Top it off with the fact that the police refused to take his disappearance seriously initially and just assumed he was lost or injured and would eventually turn up.