If rape charges have been laid then he could have done it before or after. Perhaps it was him raping her that alerted the parents for eg and led to the massacre.
Perhaps he went back to the body of chantelle (if she was murdered first) and raped her then. Or perhaps she was hiding in a cupboard, with her parents being killed first, then her being raped and killed next.
Without any firm details it's impossible to tell. A local has stated that the rape charges are true, and a scottish paper has also reported it. It is puzzling that no australian papers seem to include rape amongst the charges. Perhaps that was what the suppression order was all about, although i cant really fathom why.