Please, bear with me a little here.
When I post I am actually thinking out loud so if my posts seem a little rattled its because I am reasoning as I type.
If I am understanding things correctly...
Brittney's phone pings on 5/30 between 8:20 and 11:20 in the Rosinton Styx River area.
Donnie's phone also had activity at the same time and I assume from the same area, right?
This location is just down the road from Donnie's Styx River home so it stands to reason that they were actually at the home at the time.
Donnie's home is on or near Water World Road.
The police actually did a search of the area, right?
Okay, lets assume for a moment that Donnie killed her at or near his home.
What is his next step?
If he puts the body in his truck and proceeds left on Water World, he comes up to Hwy. 64 and the Oasis Truck stop.
Which also means that there's a good chance that there are people around. He would know this so I think (if he in fact did kill her there) he went right on Water World toward the Styx River shooting center. There are only a few homes in that direction.
The only other alternative is if he did go left, he would likely turn north down the little trail that leads to the wooded area near the Styx river just west of the indicator of Brittney's cell phone ping on the Satellite map. That road circles all the way around and comes out at the shooting center.
I would definitely search the length of that road for her body if it had not been done yet.
At midnight on the 31st, Donnie leaves the area headed back toward Tillmans Corner.
If he did kill her, I assume he took her phone with him to make sure it is not found at his home. So, is he smart enough to have removed the battery from her phone to avoid it pinging on the way?
I don't know.
His phone pings at Tillman at 1:00 AM
Hers pings at 1:37 from about 15 miles away at Grand Bay.
Inexplicably the same text message gets sent that was sent at 11:20?
That doesn't make any sense.
If he is smart enough to remove the battery, its conceivable that he disposed of her phone near Grand Bay after sending the text, which would also prevent any pings headed back toward Tillman.
Since the battery was found in his truck, maybe he just absentmindedly forgot to dispose of it.
To cover his tracks, he keeps trying to contact her, to no avail.
Pardon my rambling, but its how I formulate hypotheses in these types of cases.