I think they are starting with the 8 mile radius because they have profiled JM as not very cautious/overly confident:
1. He had been accused of TWO rapes already, prior to the 2005 rape--yet, he did not get punished.
2. Then, he was not cautious in the 2005 fairfax rape (assuming that it was him)--not only was he close enough for a passerby, but he let the victim see him closely enough for a very good sketch of him. But, again, did not get caught.
3. His own friends told him he looked like the sketch. Rather than flee the county, the state, the country, he simply added some hair--and continued to violate victims. But, he did not get caught.
4. Then, despite having already been "ID'ed" by friends, he dumped MH only a few miles from where he used to live (ponderosa trail), 10 miles from where she was last seen, and then listed his place of business in 2010 as the same address on ponderosa trail. Careless; yet, still, he did not get caught.
5. Finally (though there may have been others), we get to Hannah. He has already been called out by friends as looking like the sketch that is now linked to both a rape AND a murder. Yet still, he was careless or cocky enough to be seen on video with Hannah, AND be seen at a bar with her by people who know him well. This is the first time he can positively be identified as the last person to be with his (presumed) victim.
6. Then, EVEN AFTER he was ID'ed publicly as a person of interest, he drove to the police station.
I see no reason for LE to think he would have then traveled far distances to dispose of her. I think JM did not, at the point of HG's disappearance, believe he was anything other than invincible.
I think there was a very clear moment when it finally occurred to him that he might be in trouble--when he fled; long after he had already disposed of her. And even then, he was careless. He fled in his own sister's car, in a fairly straight line, and tried to hide out in the middle of other people (surely there was some secluded rural spot where he could have slept on the side of a road, or on a park bench in a big city?)
There is some reason why LE is making this an 8 mi radius or is it by default?
I am trying to approach this by thinking about what likely happened after he and Hannah got into the car from Tempo's.
I am reasonably certain that he got her to come with him, get into his car because she thinks he will just drop her off, and it's only minutes away, is it not, where she lives, where she was partying?
She's an intelligent womna, Even drunk, I would think she'd notice pretty quickly, like within 10 minutes that something is wrong. JM is not heading to where she wants to go.
What to happen at that point of realization? JM is in that cramped, crappy car, he's a big guy, not much room to maneuver. She's a tall girl, nearly 6 feet tall in the other seat, she realizes he's not taking her home. What would have to happen to keep her in that car? How do you abduct someone from downtown Charlotteville ? Where to go, what to do?
He must have known about some places nearby. I have a feeling they are private so LE hasn't checked them. JM would likely know that these are not places LE would search. Safe from the dogs, safe from the search. Owner is one who doesn't care about the property. What places are like that within a 5-10 minute drive from Tempo at 2 AM? Has to have reasonable road to get in there given that beater car, but out of sight, and most people would not go in there. Can any one circle around Tempo and come up with a list of such places?
I wish we knew if the cadaver dogs got a hit on JM's car. If they did not, that is likely the where she is. He's impulsive, impatient, in a hurry, horney, needs to get her where ever quickly, make his score fast. I think she's near by, near Tempo.