"Your heart cannot help but go out to the Banerjee family. By all accounts Aryan was a bright and bubbly boy and his loss in such a senseless way is unbearably sad," Mr Stewart said.
"But in the end Aryan's death was not something that anyone could have reasonably seen coming. WorkSafe's enquiries have not turned up any similar incidents involving a window latch handle in New Zealand."
Mr Stewart said although it was possible to foresee that someone might have found themselves stuck in the toilet, "it was not reasonable to think the school or the worker involved should have planned to avoid the possibility of someone being so seriously injured climbing out a ground floor window and being caught on the latch".
"I know the investigation process has been tough for the Banerjees but it was important to take the time to look into this matter and the legal issues surrounding it thoroughly," Mr Stewart said.
WorkSafe informed Aryan's family on Friday about the outcome. The school had also been notified.
His death will now be the subject of a coroner's inquest to formally determine the cause of death.