Taylor and Darcy had been paddle boarding at Avoca lagoon and swimming, at some point the child had hit his head and had ben submerged for at least one second.
The next day, Darcy was dead.
“Adam Taylor has more of a story to tell about that,' Mr Dillon said, '(This) troubling and suspicious set of circumstances remains unresolved,” Deputy State Coroner Hugh Dillon told 60 Minutes.
Despite this, there was no evidence found that Mr Taylor had caused Darcy any harm.
One of the doctors who treated Darcy told the inquest that there was strong evidence suggesting the boy had been assaulted or "thrashed" and received a blow to the head, reports SMH.
"I know that he was boxed on the ears probably that day, " Dr Wilkins said. "He died consequently."
Mr Atkinson described the moment the doctors told him their was nothing they could do.
"They started explaining that Darcy's eyes had dilated and they weren't able to contract or anything like that," grieving father told 60 Minutes.
"I was hanging onto hope and I just wanted to get back into Darcy and take him and run home with him.
"When you go home after burying a child you've just got nothing to live for. They hand you a cardboard box with some ashes in it and say that's what you get out of all, everything that's happened, and you think, 'they've ripped my whole life apart and given me this bag of sand and told me to bury it'."
Darcy’s mother says she still dreams about her son everyday.
"He cuddles me tells me he misses me and it feels really real," Ms Maxwell said, fighting back the tears.
"It just kills me, it kills us. I'm probably going to die not knowing what happened to him."