Just a few thoughts.
1. About that lunch box. If *he* threw it from the car, there may be prints. Also, you might be able to tell the direction of travel - if he threw it from the driver's side, he was traveling on the opposite side of the street; if she threw it from the passenger side, they were traveling on the same side of the street. It will be about fingerprints; if there are some which cannot be determined to be Holly or someone who would've touched the box (e.g. Mom, Dad), then it's a good chance it's the bad guy's prints. Which also gives them something to run with, if there are enough comparison points and a record of the prints.
2. You would be amazed at how much blood a human can lose and still be all right - something along the lines of 2-2.5 liters. Huge amount, when spread around...so blood by the door does not mean she was incapacitated. As has been said upthread, she could've taken a pop to the noggin, and it bled a lot...but she'd still be fine, too. And if her scent was strong - which it would be, seeing it's her home - the dogs may not have found the entry point into the woods because they could not differentiate that from her living there. Dogs are good, but they are "human", and scent cones are not necessarily as easy to define as we'd like.
3. My big question would be: who else is missing from the area? Someone's brother, father, son may not have come back to their normal lives...I'd ask the TBI if they've gotten any missing male reports, or if they've started canvassing surrounding areas for sudden disappearances from work, school, or other "regular" attendence. While this may not be anything, if - **if** - this is an ongoing abduction, then there is someone else...and they won't likely be going about their normal daily lives. If one can pinpoint that, one may have a good lead. Of course, if this is an abduction and murder, then the bad guy would only have been missing a short while, and the above doesn't apply. But if not - and there are indications that this is not a typical "snatch and kill" type of incident, then I'd be asking for help from my community and the surrounding ones about suspicious disappearances, and even those who may have said "I'm on spring break/taking a vacation" for the week or so. It's a lead to follow, at least, until something else proves more reliable.
4. I don't believe the brother was involved. I can easily imagine a time where, had me and my brother lived in the same place, he'd see/hear something that would not trigger his suspicions, but would have been an issue for me...brothers and sisters of that age tend to "live and let live" regarding siblings and their activities. He may have thought she was cutting school, running off into the woods with someone for an encounter, a picnic, or anything "away" from school and life. Believe me, while in RN school, I often contemplated how I could 'cut' school...and avoid the world for the day. She may have said something, and the pressures in nursing school are enormous, so he easily may have thought "well, she's cutting out today. Meh, no issues...let her relax" until he found the blood...
Just some thoughts this morning. Praying for Holly, and for all the LE, searchers, and family members.
And of course, all this is MOO...
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Herding Cats