Yes, this greatly weakens the whole, "Who would have had an interest in returning and moving Meredith, and staging a sex assault?" meme.
This is why even when I factor some culpability on the part of Knox and Sollecito in (to explain various holes, questions) I am finding more and more, as the info on the murderwiki seems to be strongly refuted empirically) that I have to assign them some peripheral role ( e.g., they put Guede up to robbing MK, and became frightened when they realized the point to which he had taken things.)
Adding to my above words from my prior post, the only thing I could think of is:
1. Knox placed the duvet on MK and locked the door - nothing else. This was from being distraught and horrified that RG had done as he had.
2. Knox and Sollecito may have staged the burglary - ( for even the Postal Police believed it looked staged, prior to finding a murder had occurred on the premises) - to deflect from their having given Guede entrance via a key. (perhaps some argument/ill will had carried over from that afternoon, and from MK having distanced herself from AK on Halloween)
3. They never expected to have to explain this, and now they feel it would be too horrifying/embarrassing when so many have viewed them as completely innocent . When a person is murdered, anyone having been part of a criminal plan (robbery) which led to that act would be culpable as an accessory. Not to mention lying to police, staging a crime scene, obstruction of justice, hampering a murder investigation... (Imagine what their parents and the Kerchers would think, as well; and having been part of such a prank/crime would do nothing for their future reputations/careers, either .)
4. Perhaps (if they had anything to do with it at all) they simply had wanted Guede to rob an empty cottage, and MK came home unexpectedly early.
5. Perhaps the piercing scream heard that night was Amanda finding that Guede had murdered MK. (I always felt this, intuitively, for some reason.)
***In any event, I think the above is a lot easier to believe than that 3 attacked MK but all the evidence keeps pointing to one.
( all speculation only, of course - and I might add, all cooked up only because so much of the strong evidence I had found on the wiki has dissolved and been empirically explained away--and if Halkides is correct that the luminol reacted to something other than blood, and the mixed blood prints/traces are actually not that, and not from the crime night - if not, then there are pieces of evidence pointing to MK/AK bleeding together; and if multiple attackers theory is true, this would place them back at the crime scene when the murder occurred. )