Well the Guatamalan Nacional is treating it as a homicide. So there must be clear visual evidence on her body to arrive at such a conclusion so quickly after her body had been discovered.
It may not be as clear to determine whether Catherine had been raped or not, but I'd imagine even for Guatamala, (which is a third world country) that would be fairly straight forward to confirm after a basic postmortem.
As I say, if she's been murdered up there its hard to see any other motive other than one that is sexual.