BBM.
IIRC, wasn't there a boot print in the dust on the balcony that was later thought to belong to a LEO who was on the scene before official photographs were taken? I'm sorry-- I don't have a link handy, but maybe someone else does.
If I'm remembering that correctly, then that is documented proof that there was contamination of the scene. Contamination is not necessarily a bad thing-- officers and other officials doing their jobs often have to enter and interact with a crime scene for safety, to investigate, retrieve evidence, retrieve bodies, etc. The more important thing is to conclusively determine what is contamination, and what isn't. That is why official photographs are taken to document and preserve the scene at the earliest opportunity. Contamination can also occur from natural occurences, weather, etc. If it had rained after Rebecca's feet were in contact with the balcony, for instance, the dust on the balcony would have been further disturbed and contaminated.
It sounds to me as though there is not agreement among experts as to the nature of the footprints in the dust. There is a conclusion by LE that may or may not be accurate. If the case ever is reinvestigated, or goes to trial, many experts will be consulted for their opinions.
I don't think it's accurate to declare that "the scene wasn't contaminated", as though that is definitive. It may be a valid personal opinion, though.