The defence lawyer of a man convicted of second-degree murder in the 2004 death of his girlfriend's toddler is arguing it was unreasonable a jury found him guilty.

James Paul Turpin, a Charlo, N.B., man in his late 30s, was sentenced to life in prison with no chance of parole for 10 years in 2016. He is appealing the conviction.

A jury found Turpin guilty in the death of the two-year-old, who suffered a fatal brain injury while in his care. Turpin maintains the toddler was injured when she fell in the bathtub and hit her head.

Margaret Gallagher, Turpin's legal aid lawyer, argued to the Court of Appeal on Tuesday that the level of uncertainty displayed by the Crown's 12 expert witnesses during the trial creates reasonable doubt.

Kennedy Corrigan

Two-year-old Kennedy Corrigan suffered a massive brain injury on April 2, 2004, and died a week later at the IWK Hospital in Halifax. (Court exhibit)

Gallagher said "all the experts said it was basically undetermined" as to what lead to the injury that caused Corrigan's death.

"If the doctors can't decide what happened, how can a jury decide beyond a reasonable doubt?" she told the court.

Defence argues judge erred

Gallagher was also critical of Judge Judy Clendening's actions — or inaction — during the trial.

She said the judge should have warned jurors to ignore the comments of staff that Turpin was behaving '"bizarrely" when he was at the hospital, saying there is "no predictability of behaviour" in extreme situations.

She said Clendening didn't properly employ her "gatekeeping function" to reduce the number of Crown witnesses. The dozen experts more than doubled the standard allotted number of five.

Crown prosecutor Kathryn Gregory said the "seriousness of the injuries in the context of other evidence" makes a second-degree murder conviction reasonable.

"The potential of unreasonable doubt does not equate with an unreasonable verdict," she said.

James Turpin

James Turpin is seen outside the Fredericton court house while still in police custody in this file photo. (CBC)

During the three-week trial, the Crown argued Turpin inflicted the brain injury in some fashion, such as by shaking Kennedy, striking her or throwing her to the floor.

As for the dozen expert witnesses, Gregory said there were never more than five testifying in any one area of expertise.

'Hard time making the jump'

On Tuesday, Justice Marc Richard said during the Crown's arguments, "none of those witnesses spoke of intent...To me, I have a hard time making the jump.

"Most of the time when you are asking someone to infer intent, you know what happened," Richard said.

"Here you have to infer what happened, and then you infer what happened, and then from the inference that you've drawn, you're asked them to go a step further and to infer some more, and I see a danger in that. You don't?"

Fredericton court

The Fredericton courthouse. (CBC)

The Court of Appeal can uphold the verdict, lower it to manslaughter, order a new trial or acquit Turpin.

Turpin was taking care of Corrigan on April 2, 2004, while her mother was at work, when the girl was rushed unconscious to the Dr. Everett Chalmers Regional Hospital in Fredericton.

Kennedy died a week later at the IWK Health Centre in Halifax after being taken off life support systems without regaining consciousness.

No charges were laid at the time, but the RCMP's historical homicide unit reopened the case in 2013, and Turpin was charged in 2015.

With files from Catherine Harrop