The 31-year-old declined to give a statement to police - as is his right -but neighbours, paramedics and other emergency responders told the jury what they heard him say that night.
Some said Mr Archer told them he was swinging Ariah around when she slipped from his grip and hit her head on a wall while others recalled him saying he was throwing the girl when he dropped her.
Professor Colin Smith, a neuropathologist in Scotland, told the jury the pattern of bruising, including two notable bruises on the right side of her head and the base of her skull, suggested more than one impact.
Dr Rexson Tse, the pathologist who completed the post mortem, said the toddler's injuries were classic features of abusive head trauma.
He said bruising around both ears as seen in Ariah's case was rare, occurring in one in 1000 children, and it was unlikely the force applied to her head was accidental.
In his closing address, Crown prosecutor Brian Dickey held up a series of exhibit photographs which documented Ariah's injuries to the jury.
"No child should look like that, no child. None in a thousand did when they did the longitudinal study that Dr Tse referred too.
"[There are bruises on] the back of her head, the top of her head, both sides of her head, underneath her chin. This child has been badly abused."
Dr Rexson Tse, the pathologist who completed the post mortem, said the toddler's injuries were classic features of abusive head trauma.
Ariah's family members have told the court the toddler had tumbles while learning to walk and was known to bang her head against the wooden rails of her bedroom cot.
Mr Dickey said the toddler must have been "one very unlucky girl" if the jury were to believe she wasn't the victim of a fatal assault."
"The proposition is perhaps she was the unfortunate subject of a great many accidental events which caused bruising to [her head and face].
"And, being the unfortunate sufferer of these accidents, you know what else happened to her? Terrible stuff. She was accidentally slammed against a wall. Accidentally."
Mr Dickey asked why Mr Archer would swing the toddler inside their home; a modest two-bedroom batch with a small living area.
"What on this living earth would motivate you to swing a child inside that house in a way that would permit her head to be slammed against a wall, floor or coffee table?"
He told the jury they may also ask why the defendant didn't call an ambulance, why he covered the child in her mother's dressing gown and why he didn't have a consistent explanation about what happened.
"The case, considered dispassionately and objectively against the reliable evidence, is that it was deliberate. Almost too awful to contemplate because who can contemplate that."
The defence team led by Ron Mansfield, called their own expert witness, Miami-based forensic pathologist Dr David Garavan, in the trial's second week.
Dr Garavan told the court Mr Archer's explanation of events did explain Ariah's injuries; noting he could only say they indicated at least one impact, not more than one impact.
Initially called as a Crown witness, Ariah's mother said she washed the girl's hair the night before she died and didn't notice any bruising on her head.
But she was recalled by the court after her own mother, Ariah's maternal grandmother, told the court Ariah's head was covered in bruises.
During her second appearance in the witness box, the girl's mother confirmed there was bruising on Ariah's head but said it was from the girl banging her head on her cot and standard toddler tumbles.
Dr Garavan said the sum of Ariah's bruises could be explained by normal knocks, her body being handled during resuscitation attempts and a single impact to the head.
However, he conceded under cross-examination that the bruising around both of the girl's ears was unusual and would require an explanation.
Mr Mansfield said the expert evidence confirmed it could not be ruled out that Ariah's injuries, even the two substantial bruises, were accidentally inflicted.
He told the jury his client's explanation and demeanour was entirely consistent with an innocent person and questioned why Mr Archer, who was described by Ariah's mother as an otherwise loving and supportive partner, would want to kill the girl.
"He acknowledged from the outset that he was involved, that he was responsible but that it was an accident..the reality is anyone involved in an accident like that is human and they react with emotion; without thinking through the most sensible first step."
Last week the jury heard a voicemail Mr Archer left on Ariah's mother phone when she didn't pick up his call.
In it, he can be heard vomiting, wailing in distress and repeatedly screaming Ariah's name, "no", and "I'm sorry".
Mr Dickey had said Mr Archer's distress did not account for what happened in the minutes preceding the call but Mr Mansfield said it laid bare just how distraught his client was.
"This is an incredibly sad case but when you look at the evidence dispassionately you see it's not just possible but likely that what Mr Archer said occurred did occur."
Mr Mansfield said there was a "complete absence" of any evidence of murder and asked the jury to use reason and logic when considering their verdict.
"Please, be shocked, be angry, be sad, maybe even harbour hatred for the stupidity of the man for swinging the child inside that room but don't use that emotion rather than the evidence you have to convict a man of murder who has not committed murder."
