How sure are you that Stefanoni never changed her gloves at the crime scene? Have you seen the complete footage of the video Bruce linked showing she did not change gloves? Can you list the items you feel were compromised by Stefanoni's neglect? And, lastly, what other items of evidence were taken in or swabbed the day the bra clasp was collected?
I have examined several hours of video, and no one ever changes gloves. If they did so, it was off-camera. Here is a pair of gloves captured in a photo of the kitchen taken on December 18, 2007:
http://www.friendsofamanda.org/kitchen_dec_18_07_closeup_of_gloves.jpg
You can see that the fingers are covered with grime.
Here is a sequence of frames captured from police video, showing Stefanoni's procedure for swabbing a sample:
http://www.friendsofamanda.org/stefanoni_swabbing.jpg
In the first frame, she is scrubbing the blood spot with the tip of the swab pointed to the right. In the middle frame, the tip of the swab has been folded back so it points to the left. In the final frame, her thumb bears down on the blood spot on the swab.
I have had the opportunity to review this material with a DNA expert, who confirms the obvious fact that the procedures displayed in this video are highly likely to cause transfer of DNA between samples.
Now, what are the practical implications of this poor procedure? I think it is the most plausible explanation for the screwy results shown in Samples 176 and 177, which were swabs of the floor in Filomena's room, collected on December 18, after investigators used their luminol. They got the footprint images that we have all seen. They also got a reaction in Filomena's room, which was not a shape but rather a diffuse glow in a general area. Sample 176 clearly showed Meredith's DNA with faint markers corresponding to Amanda's profile. Sample 177 clearly showed the DNA of both Meredith and Amanda. Both samples also showed other markers as well, probably those of Filomena, for whom they did not bother to collect a reference DNA sample.
How are we to explain this result? I think the most likely answer is that luminol was applied at the very end of the investigation on December 18, and the material on Samples 176 and 177 was from the fingertips of gloves that had handled other samples containing the DNA of Meredith and Amanda.