If he has six alibi witnesses, he still has plenty of time to kill Katelyn and dispose of her, but then the text messages from her phone are problematic.
Not necessarily. As I said earlier in my "if he did it" scenario...
He takes her phone with him to the friend's house. While there, he texts KM's phone and says the documents have been burned. Then he surreptitiously answers himself from KM's phone - perhaps while in the bathroom, or in the woods for a wee if the friend's place is rural, or even just while stepping away from the firepit.
In the dark, from a distance of a few feet, no one would notice he's not texting from his own phone - he'd just look like he was texting.
He wouldn't even have to go out of sight. He could just wander around, near or far from the fire (if there was one), and slip each phone from his pocket as he needed it, thus appearing to be innocently texting.
After a couple texts back and forth, he looks through the pics stored on KM's phone and chooses one to send as the last text. Then he turns her phone off, and/or GPS off, and/or removes the battery. He then "receives" the pic on his own phone. Maybe he even shows her picture to a friend he's standing next to ("look what she sent me, doesn't she look pretty"), to establish with a witness that KM's in communication with him and they're not fighting.
After leaving the friend's, he easily disposes of her phone and the battery in any of a thousand possible places where it may never be found again.
OR...
OR...
Suppose cellphone records show the text conversation really did go back and forth between his location (assuming it was in the radius of a different cellphone tower) and Katelyn's townhome, then there are 3 options I can think of:
1) The texts really were from her, and harm came to her later that night.
2) JC had an accomplice at KM's location pretending to be her.
3) JC pre-scheduled some texts to send from her phone to his at certain set times, and then he left, and "got" the texts at the other location, answering them appropriately.
2 and 3 seem a bit convoluted, but they're possible.
I'm very very curious about what the "pinging" records say.