Why would luminol destroy the DNA in the corridor but not in Filomena's room, or for that matter, in Amanda's room where Amanda's DNA was found in the footprint that showed up with luminol? Or in Sollecito's apartment, where his DNA was found mixed with Amanda's in stains that showed up under luminol?
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You're capable of doing the same googling as I, Charlie. (Well, no, I remember two summers ago, you were incapable of following my google instructions to find some positive information about Giuliano Mignini. More than incapable, you simply refused to do it).
If you google around regarding luminol, you'll see that the degree to which the luminol destroys the organic material depends on a number of factors, including the state of each testing sample (here's an observation on my part, I don't know if this explains the lack of DNA in the hall, and the preservation of DNA in Filomena's and Amanda's rooms, but the hallway was like Grand Central Station on the morning of Nov.2, with Amanda, Raffaele, 2 cops, 2 Italian girls, 2 Italian boyfriends all huddling about, moving, dragging their feet, taking a stance to knock down the door, being ushered out .... Filomena's and Amanda's floors didn't get that treatment).
Also, we're not aware of the dimensions or form of the DNA mix in Filomena's room. We understand it's not a footprint, so the luminol could spot the location of the mix, and the swabbing be done in an adjacent point.
In any case, it's not always black or white, "if you use luminol, then there's always a total loss of further organic testing".
Try this site, it's amazing:
www.google.com