He described the injuries found as "significant" and not the type he would expect to see in what he termed a low-level fall, such as from a bed.
"We are looking at a level of force of the type seen in car accidents or a fall from a height."
In his opinion, all the bleeding the post mortem uncovered happened at the same time and came from fresh injuries.
"She [Maija] succumbed to this acute head injury very quickly," Smith told the jury of seven men and five women, saying even if a neurosurgeon had been close by she couldn't have been saved.
Asked by Gordon what time frame he was referring to, Smith said at the most she'd have lived from one to two hours, but probably survived for just a few minutes.
He disputed any suggestion the injuries had been sustained in a fall up to two weeks before her death, emphasising neuropathology evidence was inconsistent with that.
In his view there had been no "stack up" of previous head injuries the child suffered; rather they were mild, individual events which didn't produce a cumulative effect.
He also debunked a suggestion they could have been caused if the infant had been smothered while co-sleeping with an adult.
In a DVD police interview played to the jury earlier in the week, Duff recounted how, the day before his daughter's death, he had woken to hear her crying from under him and feared he had rolled on her in his sleep.
Asked if Maija could have survived if she had got prompt medical attention, Smith was certain she couldn't have.
"I think that's very unlikely, I think she succumbed very quickly to these injuries. She sustained a devastating head injury that's been fatal very quickly. "
Questioned by Duff's lawyer, Moana Dorset, he agreed no science was exact but was confident his evidence pinpointed the most likely scenario surrounding Maija's death.
Evidence from a further 13 witnesses was read which Justice Mathew Downes said he was grateful to the lawyers for, explaining to the jury it considerably shortened the trial process.
Urging jurors to put the trial out of their heads the best they could over the weekend, he adjourned proceedings until Monday when the final Crown witness, an US-based paediatrician, is scheduled to testify.