From all accounts Stephanie was a very nice friendly person, teachers often stay back working when cleaners are on site, so it's quite likely they did know each other. My guess is he has developed an infatuation with this young beautiful friendly teacher, who was probably quite kind to him.
My theory is, she was at school and he was driving by the school. He sees her car and considers this might be an opportunity to attack her, or maybe just to talk to her. The conversation would naturally be about her doing her handover because she is getting married in a week and going on her honeymoon. My guess is he was quite jealous of the fiancee, and it's quite possible she told him the Fiancee was not at home, ie, had attended a party last night and she was finishing up some work. This is around 1pm as she sent the last email.
So he made and move, she fought back and during the struggle he killed her. He knows hes got a few hours at least until the Fiancee will be back. He would move his ute close to the school (the carpark is on grounds), then place her body in the tray hidden beneath the canopy. He takes her laptop and car keys and drives the Mazda out into the vineyard off a dirt track. He walks/jogs back into town to school, cleans up any visible evidence quickly, then leaves the school. This would be about 3-4pm.
He then drives the ute somewhere remote on sunday afternoon, my guess would be somewhere in the bushland near the river near the village of Yanco. He burns the body to try and hide any DNA evidence, and for some ****ed up reason takes some pictures of her. May have then buried her in a shallow grave. He also throws her laptop/phone? into the channel, he may of thought it could be traced somehow.
Back home by 7:20PM as that seems to line up with witness reports of the time he arrived home.
I just wish he would, even if he didn't admit to the crime, at least just tell the police where her body is so the family can bury their loved one.
