Going by the limited information so far...
I think his version of events have "partial" truth.
IE: She was being bullied. That they did drive a bit out town.
But I think he played a massive role in her death.
That perhaps he drove her to a location where the bullies met up at "said place" agreed by them prior.
Belted her to death (perhaps NOT intentionally to kill her)... BUT did.
He had to hide her body.
In the CCTV footage of his car 6kms out from where her body was found... it looked like that car was driving like a bat out of hell!
Small towns are notorious for bullying. And worst of all, there's no escaping it. (Personal experience).
Why he withdrew money from her bank account? I can't make complete sense of.
I'd think its common knowledge they have cameras.
But participating in anything like this... proves to be dimwitted, to look cool, be part of the "in crowd"... well, now he gets to be apart of "out-crowd" in jail... and I hope anyone else who participated in this... gets the justice they deserve too.
I can't help but wonder, how these parents raised their children? At the age of 18... he'd still be strongly under the influence of his upbringing.
Just my thoughts thus far into information currently given.