I believe the child killer Huntley and his wife (U.K crime) left absolutely no trace of anything once they had cleaned their house.
Huntley did leave small traces of one of the girls' blood in or around his bath, IIRC, and claimed that the girls had come to his house and one of them had had a nosebleed. And since there was no reason for either of the girls to have ever innocently visited his house at any time, and no evidence that either of them had ever been in his house before, and given the very unlikely coincidence of one of them having a nosebleed on the one and only short occasion that she'd been inside the house (let alone the upstairs bathroom), this was quite strong evidence against Huntley in its own regard.
(And BTW his partner, Maxine Carr, was never linked in any way to the murder itself, and was never charged with murder. She was, however, convicted of perverting the course of justice for providing a false alibi for Huntley - although it was accepted by the courts (IIRC) that she did so because she believed Huntley to be innocent).
But make no mistake, it's not difficult to remove incriminating forensic evidence from a crime scene and/or non-ballistics weapon (i.e. not a gun) if you are in any way methodical and know which general areas you need to clean. Even a mild bleach solution, if applied with any sort of care and accuracy, will destroy all blood and denature all DNA, leaving only a bleach residue. And it's likely that a perp could explain a bleach residue by claiming it was the simple product of regular domestic cleaning. Even a decent surfectant/disinfectant would have the same effect, but bleach would all but guarantee complete trace removal.
Similarly, latent prints are extremely easy to remove with as little as a quick wipe with a cloth - and in any case they're actually quite difficult to deposit in the first place unless the part making the print is wet with some medium such as blood.
If Knox and Sollecito HAD been conducting a post-crime clean up, it would have been trivially easy for them to have filled a bucket with a good solution of surfectant/disinfactant and/or ordinary household bleach in warm water,then mopped/wiped every surface and floor that they wanted to clean up. They would have then disposed of the dirty water down a drain, washed out the sinks/bidet/shower with hot water (and/or bleach or surfectant/disinfectant), and sat down with a cup of tea.
But anyhow, in my opinion, the very presence of visible blood drips in the bidet and sink of the small bathroom
in and of itself puts paid to any notion of a post-murder clean up. Not even a deranged and panicking first-time killer would conduct the sort of clean-up alleged by prosecutors, then either neglect or forget to clean down the sinks and bidets where there were immediately-visible blood traces. And Knox and Sollecito were supposed to have had most of the night and all the next morning to check for such blindingly-obvious things.
There was no crime scene clean-up of any description in my opinion - outside of a clear and clumsy attempt to mop up some of the blood within Meredith's room. Which was done by Guede, in my opinion. Unfortunately, we'll never have even the possibility of knowing who might have done this in-room blood mopping, since the expert Patrizia Stefanoni left the towels in question in a wet heap, causing them to mould and become useless for forensic analysis. Well done Ms Stefanoni!
