Gah, I've been here for 6 hours and still haven't caught up on this thread...and I'm racing because I know what it's like to fall behind to that never being able to catch up point. Anyway!
Thinking more about all this DNA stuff (I hope I can work this post out clearly because right now it's all just a big jumble in my head).
DNA Points/Possibilities to Ponder:
1. They have collected DNA from the crime scene area. This DNA:
A) May be related to the perp.
B) May not be related to the perp.
*Either way one can possibly conclude it has not positively matched anyone in CODIS to date.
2. So, IF DN's DNA is already in CODIS (one would assume), then:
A. The DNA referred to in #1 has not produced a hit/match to him to date (considering they have been running it, and frequently over the months, as more cases are processed and entered, as I think they would be).
3. If DN's DNA is not already in CODIS for some strange reason, the newly collected sample:
A: May produce a hit to the DNA referred to in #1.
(Case solved)
B) May not produce a hit to the DNA referred to in #1.
If this is the case, then:
aa. It could mean 1B, that the DNA collected from the crime scene is not necessarily that of the perp, so DN could still be BG.
bb. The DNA collected at the crime scene is that of BG, but doesn't match DN, therefore excluding DN as the suspect.
4.) Adding possibility of possible second perp's DNA to mix.
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I tend to wonder, maybe LE doesn't even know if they have BG's DNA.