On #1, most cell phone tower information is kept any where from 4-6 months to 12-18 months with the exception of AT&T:
How long do wireless carriers keep your data?
HOWEVER, I wonder if LE obtained the cell phone numbers that pinged on the closest towers that day? Or does that violate privacy laws? (Wow! If LE had to provide probable cause on a specific phone number to obtain a search warrant, could they be out of luck now if a suspect pops up?)
I'm wondering if his DNA doesn't match and if he has no alibi for that day LE can't rule him in OR out. Of course, Sheriff Leazenby stated in the February HLN special that they don't know if the DNA they have belongs to the killer. So if his DNA doesn't match could that mean LE can't rule him in, BUT considering the killer may have not left his DNA (or LE didn't find it) they may not be able to rule him out. (Unless he used a gun and shot the girls - without touching them at all - it would be tough to avoid leaving his DNA even through transfer from his clothing or gloves.) IOW, without a DNA match or a solid alibi his suspect/eliminated status might be in limbo.