Coroner Alexander Ho's inquest into the 2019 death of Lachie Jones began at the Invercargill District Court yesterday.
The police swiftly concluded it was an accidental drowning but Max Simpkins, the lawyer for Lachie's father Paul Jones, suggested the boy had been killed several hours before he was reported missing and a false alibi was established to cover it up.
During her two days in the witness box, she described how Lachie twice ran away from her shortly before his death and hit out at those who had criticised her.
"My whole world, my whole life has been destroyed. I've just had all these false allegations I was a bad mother, which wasn't true at all. It's just been horrible," Ms Officer said.
"I've been . . . in grief and depressed and I just don't want to live sometimes. I just want to be with my wee boy."
She told the court she had collected him from pre-school, done some work, picked up her middle son and gone home for a pizza dinner.
Later that night, Lachie had a soiled nappy but she said he played a "sort of hide-and-seek-chase game" when she tried to change him.
After he went to watch television, she tended to her other son who had a mishap with some gym equipment.
When she returned to the kitchen, the woman described seeing a flash of hi-vis out of the window.
"I just took off," Ms Officer said.
After gently reprimanding the runaway, she said he set off towards a neighbour's house, so they popped in.
As she spoke to the woman, the mother said she kept an eye on Lachie.
"I just moved forward and lost that peripheral vision for 30 seconds. It wouldn't have been long at all," she said.
It was the last time Ms Officer saw him alive.
Max Simpkins, counsel representing Mr Jones, said an expert would give evidence later in the inquest to say that the trip to the neighbour seemed designed to create a "false alibi" and that it was impossible Lachie could have rounded the corner of the road towards the ponds in such a short time.
"He was quick and he could've hid anywhere," the mother said.
As she searched for her son, Ms Officer called police from near the oxidation ponds where Lachie was ultimately found.
"You knew he was already there," he suggested.
"I didn't know where he was," she said. "You eliminate the dangers."
Mr Simpkins also highlighted claims by one of Ms Officer's friends, who said the mother had told her in the aftermath: "Lachie has done me a favour".
The tearful witness denied making such a statement.
"I'd rather drown myself than have one of my boys drown . . . it's really awful to say that to a grieving mother."
Videos of Lachie chasing ducks in an Invercargill park were played in court today and she said she was so worried about his speed and fearlessness she had bought a safety harness for him.
"You had to hold him and say 'Lachie, don't fall into the water' and I don't think he understood the hazards. He just wasn't at that age where he got it," Ms Officer said.
"It made me anxious because he was really confident. He'd just run off . . . he could climb really easy and he was a fast runner."
Statements obtained by police from neighbours and pre-school staff described her as an attentive mother, bordering on over-protective.
Her two sons - Lachie's half-brothers - loved him, Ms Officer said.
"They used to sing and dance with him. They just thought he was so funny and so entertaining."
But Mr Simpkins said her sons had assaulted Lachie.
The woman said one of the incidents, in which the boy hit his head and was taken to hospital, was an accident.
Mr Simpkins suggested the woman's other children despised Mr Jones, her estranged on-off partner of five years, and had reason to get rid of their brother.
"If Lachie is no longer at home there's no need for Paul to go to the home, is there?" he asked.
"I know what you're getting at," Ms Officer said. "My boys have a father that lives close by. If Paul comes to the house they just go to their father's home."
Mr Simpkins took Lachie's mother through the boy's medical history - ranging from nappy rash and gum disease to suspected pneumonia - and said an expert had reviewed the file and opined it showed evidence of neglect.
She vehemently denied the accusation.
Finally, Mr Simpkins put it to the witness that Lachie had been killed early in the afternoon shortly after being collected from daycare, rather than drowning in the ponds some time after 9pm.
Ms Officer described the proposition as "ludicrous".
Police believed the boy had walked the 1.2km from where he was last seen in Salford St and tragically drowned but a review later found there were "missed steps" during those early inquiries.
Counsel assisting the coroner Simon Mount KC acknowledged how the case had gripped the community.
"How can it be that a three-and-a-half-year-old boy runs away 1.2km, nine o'clock at night, dirty nappy, climbs a fence, travels across some pretty uncomfortable ground . . . through the vegetation, no one out searching sees him, he doesn't respond to anyone calling out his name, the police dog doesn't pick up the scent until quite close to him. Do you understand why people say this doesn't add up?" he said.
Ms Officer said there was nothing she could add to assist further.
The coroner opened the hearing yesterday emphasising that while two police investigations found there was no nefarious involvement of any other person in the boy's death, he was not bound by that.
"Here, we're conducting a fact-finding exercise," Mr Ho said.
The inquiry will consider the cause of death and the circumstances that led to Lachie ending up in the pond, including whether neglect was involved, and the coroner may make recommendations to prevent similar deaths.
One of Lachie's half-brothers will give evidence tomorrow.
