Someone suggested this idea on another forum; interesting theory:
"Regarding how did he know she was there, I believe we may find out that the colleague she collected keys from to the school was him. That the LE questioned him and he said something like that he gave her the keys and she never returned them ... and that he left to go camping. But that the mobile phone triangulation proved him a liar and that when they turned up there Wednesday night they found the keys on him. It's a small country town so it's possible Stephanie was referred to collect keys from the cleaner's house. And that's what led LE to follow him up in the first place. This idea was prompted by my Sydney based teacher friend telling me they are advised to arrange to be at school after hourd when the cleaners or General admin staff are there...for tge teachers' safety...and that got me thinkin did she check with him casually when he would be at school so he is tipped off....or indeed did she actually get keys from him at his house...and that's why his mother knows to help LE. Very sad for all."
24 year old picked up in SA as accessory after the fact, I assume that's the twin brother right?
The charge brought against [the accused] is that [he/she] assisted [the principal offender] after [he/she] committed the crime of [nature of crime] and gave that assistance with knowledge that [the principal offender] had committed that crime.
Wow. This is an interesting development. I don't think the twin was in the vicinity physically, so I supposed his involvement is in the coercion or instruction of his brother. Perhaps after the fact.