I have heard talking heads say there is not DNA in all of the fluids, ie if it is from the purge stage would not be DNA testable in it. I have not found that stated from a credible source and I have done a ton of searching. DNA is not in feces, and obviously purge expelled via the rectum where most of it exits would have feces, but most of the sites also say it would have blood in it and we all know DNA has blood in it so I am throughly confused by the claim that purge is not a DNA source.
As far as a pressure imprint, 35 lbs of dead weight could leave an imprint. Someone used a duraflame box as a 35 lb weight comparision, left for 3 days a duraflame box would imprint some carpet. They also may be seeing the outline of her body with a blacklight.