But today, at the end of the second week of coroner Alexander Ho's inquest into the death of three-year-old Lachie Jones, Sergeant Hua Tamariki acknowledged he may have been wrong.
In January 2019, police concluded the boy had drowned after he was found face-up in an oxidation pond 0.7 miles (1.2 km) from his home on January 29.
Two other police officers believed Sergeant Tamariki was the officer in charge of the investigation, but he was “clearly” convinced this was not the case.
“It's not a commitment I would have made,” Sergeant Tamariki said.
“Until now I believed that my role in the [investigation] was O.C [officer in charge] of general questions.”
He was involved in reporting the death to the coroner and said he believed the sloping walls and slippery surface of the ponds would mean someone would not be able to get out if they fell in.
“It is almost impossible to climb out if you fall in – adult or child,” wrote Sergeant Tamariki.
Counsel assisting the coroner Simon Mount, KC, said the water was about 36cm deep near the edge of the pond.
“There's not an adult who can't climb out of the water, it's only a foot deep,” he said.
The witness agreed.
In January 2019, Lachie was measured to be one meter long.
In a police report, Sergeant Tamariki wrote: “Lachie's diaper may have kept him upright.”
The inquest heard that the toddler's diaper was soiled and heavy when it was found.
“I'm not sure where I got that information,” Sergeant Tamariki said.
He explained that the information may have come from the local CIB or other officials.
The report to the coroner also said the death was not suspicious and that Sergeant Tamariki's name was on the form.
“I don't remember making the decision to say it's not suspicious,” he said today.
“I didn't have the skills to make such a decision with confidence.”
Sergeant Tamarki said police had learned lessons from the investigation into Lachie's death and he believed Gore should have had more staff.
He said officers often had to share the burden of a case, meaning the leadership structure was sometimes unclear.
The investigation will resume on Monday.