Before Darcey and Chloe Conley died in 60-degree temperatures inside a locked car, authorities failed to heed warnings the toddlers were at risk and prematurely closed their file on the children, an ABC investigation reveals.

Peter has just bought cigarettes at his local Friendly Grocer on a searing November day in Crestmead, south of Brisbane, when he gets the call that blows up his world.

It comes up as a private number, but it's Kerri-Ann, the mother of his two-year-old daughter, Darcey.

She tells him that she forgot that she'd left Darcey and her one-year-old sister Chloe in her black Mitsubishi station wagon.

It's after 1pm and the temperature is soaring.

"How long were they in there?" he asks.

She doesn't answer, but later he would learn they'd been trapped in the car for more than nine hours, at temperatures that exceeded 61 degrees Celsius.

"Are they breathing?" he asks.

"She said, 'No'."

Peter tells her to call an ambulance and jumps in his car, racing towards Kerri-Ann's house in the nearby suburb of Waterford West.

It's a 10-minute drive but he runs every light and gets there in fewer than three.

Inside, he hears the shower running and goes straight into the bathroom.

"As I come around the corner … everything sort of went silent for a second and I'm looking at Darcey, and Darcey is looking back at me."

"Her eyes, they looked smoky."

Peter doesn't know it yet but his daughter, Darcey, is already dead. So too is her little sister.

The full story behind this devastating double tragedy which shocked Australia three years ago has never been told – until now.

Through interviews with family members who are speaking publicly for the first time and internal government sources, we piece together the slow build-up to the girls' deaths and ask, could they have been prevented?

Pumpkin

Darcey-Helen Conley is born on Mother's Day 2017.

Kerri-Ann has a difficult labour that ends in emergency surgery, so she and Peter must wait a little before getting a first cuddle with their baby girl.

She's yellow with jaundice, and they give her the nickname, Pumpkin.

The year before, Peter and Kerri-Ann had been introduced by a mutual friend.

Peter, a single dad of two teenagers in his late thirties, had moved into a new home and was surrounded by boxes when the friend brought 24-year-old Kerri-Ann over.

Peter was immediately taken with this "blonde-haired, blue-eyed stunner". She's outdoorsy and adventurous and has travelled around Australia doing odd jobs. The pair share a love of fishing and four-wheel-driving.

When Darcey is born, they enjoy the first heady few days at home.

"Those blue eyes, they'd look straight through you. If she wanted something … she got it," Peter says.

The newborn bubble doesn't last long.

Four days after bringing Darcey home from hospital, she tells Peter she has to help a friend move a dishwasher at 11:00pm.

Peter urges Kerri-Ann to leave Darcey with him but she refuses.

"I didn't see them for three days. She wouldn't answer her phone, no text messages, nothing."

Kerri-Ann had done this kind of thing before, disappearing for nights on end.

Peter's suspicious that she's begun smoking ice again.

He had previously stumbled across a glass ice pipe and some small bags, but she denied they were hers.

After Darcey was born, Kerri-Ann's older sister Kirsty moved in to help.

Like Peter, she is becoming more and more concerned about Kerri-Ann's behaviour and Darcey's welfare.

One day, Kirsty catches Kerri-Ann in the bathroom stuffing an ice pipe down her bra.

She confronts her sister about her drug use.

"She was very secretive of what she was doing and like trying to hide the fact that she was still doing drugs and who she was with because she knew I'd lecture her and say something and try and help her," Kirsty says.

Peter and Kerri-Ann's relationship grows increasingly volatile.

He's questioning her about taking Darcey out at night in the middle of winter, while she accuses him of abuse and being controlling.

Kirsty witnesses their fights.

"In hindsight, it was actually Peter concerned for her and what she was doing, wanted her to get off drugs and pull her head in, start acting like a mother and not gallivanting around with the baby at all times of night," she says.

One morning in July 2017, Peter is getting ready to leave for his work as a long-haul truck driver when Kerri-Ann asks him to help two men load a truck with her things.

"She was moving out," Peter says.

"My heart hit the floor."

The unravelling

Kirsty and her young son move into a unit in a nearby suburb called Kingston with Kerri-Ann and two-month-old Darcey.

Like all new mums, Kirsty says her younger sister took to some parts of motherhood but not others.

"She was pretty attentive, very OCD about the way things went … people had to make sure their hands were sanitised if they tried to touch Darcey," Kirsty says.

"She always had a nappy bag, and it was all lined up with … nappies and everything had a spot and couldn't be out of place."

At other times, though, she is overwhelmed.

"Darcey could be screaming for a little bit and Kerri-Ann didn't know what to do … she'd leave me with Darcey and then disappear for a few hours."

There's trouble too when Kerri-Ann stays home.

One night, Kirsty finds Darcey screaming in bed wedged between her mother and a male friend. The pair are passed out.

But when she confronts Kerri-Ann, telling her she needs urgent help, her younger sister denies she's addicted.

"[I was fearful] she'd [Darcey] get infections from sitting in dirty nappies, that Kerri-Ann could roll over on her in her sleep if she had her in the bed with her, like if I wasn't there or no one was there … Darcey would scream all night and go hungry," she says.

Kerri-Ann's parenting grew ever more dangerous.

The night before the girls died in late 2019, a neighbour found Darcey – who was 2 by then — falling asleep in a cold bath while her mother smoked ice in the room across the hall.

In mid-late 2017, when Darcey is still only several months old, and living with Kirsty and her mother, officers from Queensland's child safety department come knocking.

The department has launched an investigation into Kerri-Ann's parenting to assess whether Darcey is safe or needs to be removed from her care.

Officers are looking into reports they have received of Kerri-Ann going out at night and using drugs with Darcey in tow.

But the investigation will take time, and the department of child safety is under-resourced.

So, their first stop-gap solution is to ask Kirsty to act as her sister's supervisor.

Kirsty, who is raising her own kindergarten-aged son, quickly becomes overwhelmed.

In the first of a series of failures, the department turns to a friend of Kerri-Ann's to share the responsibility of supervision.

However, the woman is also a drug user.

"That's when shit started really hitting the fan," Kirsty says.

The new supervisor makes no dent in Kerri-Ann's drug use.

Kirsty says at this point Kerri-Ann begins to spiral. She's "hitting the drugs harder" and refusing drug tests.

Finally, around September 2017, the department steps in.

Officers from the department of child safety turn up at Kerri-Ann's house in Kingston to take Darcey away from her.

She's placed into foster care.

In one of the many tragedies in this case, Darcey's father, Peter, is denied custody.

He discovers Kerri-Ann has made domestic violence allegations against him to the department.

Peter denies it.

"Never touched her, never," Peter says.

"She had told them that I was abusive because I raised my voice and like I said to child services, 'Of course I'm gonna raise my voice. You've got drugs around my child. Bet your arse I'm going to yell at you.'

"They told me I couldn't do that."

Queensland law prohibits prisoners being interviewed by the media.

The ABC was never able to discuss these details with Kerri-Ann but has confirmed Peter was never subject to a domestic violence order or charged with a related crime.

Peter is only given weekly one-hour visits with Darcey. He's heartbroken.

New normal

Under pressure from Peter and her family, Kerri-Ann stays with Peter for a short time to get clean.

She returns several clean drug tests, which convinces the department of child safety to return seven-month-old Darcey in early December 2017.

Kerri-Ann is staying at home, she's playing with Darcey and it seems she's stopped using.

Shortly after Darcey is returned, they celebrate her first Christmas at Peter's mother's house.

Deann – known as Nanna – says she's "the cutest thing" she's ever seen.

"She was so tiny and happy, and I picked her up and she sort of felt comfortable because I think she knew I was Nanna," Deann says.

"I just fell in love with her because she looks so much like Peter and his kids … that was a fantastic day."

With Kerri-Ann improved, visits and drug tests from overstretched child safety officers become less frequent.

She becomes difficult for Peter to contact, and he doesn't see Darcey for a couple of months

One February afternoon, Kerri-Ann calls Peter with news. She's pregnant, but he's not the father.

During her pregnancy, child safety continues working with Kerri-Ann on their existing voluntary arrangement — called an intervention with parental agreement (IPA) — for another six months.

But in July 2018, it closes the case when she withdraws her consent to work with the department.

Chloe-Ann Louise Conley is born on October 10, 2018.

Peter and Kerri-Ann decide to look after the girls together.

Kerri-Ann lives in her own house with the girls, and Peter has Darcey on weekends. Kerri-Ann and Chloe stay sometimes too.

Peter has a nickname for all of his children, and Chloe's is "the kid."

As Chloe grows, her personality starts to shine through too.

"She would basically copy everything Darcey would do … she had the blonde hair and blue eyes too, a cheeky, cheeky smile," he says.

Darcey gets another nickname, 'Curly Fry', a reference to the big ringlets in her hair.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume.

She loves being a big sister.

He smiles as he remembers how Darcey would pull Chloe around on a trailer hitched to her trike "for hours on end".

"And you'd just hear them laughing, giggling until they were thirsty or hungry and they'd have something to eat and then back on the bike."

Peter's fight for the girls

By the time Darcey is 2 years old and Chloe is 1, a familiar darkness has crept back into their home where they live with their mother.

On Saturday, November 2, 2019, Peter discovers the aftermath of a drug party at Kerri-Ann's when he arrives to pick up the girls for their weekly visit.

He takes Darcey with him. He tries to take Chloe too, but Kerri-Ann won't let him.

The next morning at 7:30am, his phone pings with a text message which still haunts him. Kerri-Ann had put Chloe in the car the night before, ready to drive to his house, then went inside and fell asleep.

He's immediately beside himself with fear.

It wasn't the first time something like this had happened. Peter doesn't know it yet, but Kerri-Ann's sister Kirsty had also reported her for leaving Chloe in the car for hours overnight.

Peter's also worried Darcey's been exposed to drugs because she's unusually hyperactive and banging her head on the walls.

He takes her to a doctor who makes a report to child safety with concerns that Darcey has been exposed to methamphetamines.

Over the next few days, he and his family repeatedly report to child safety that they have a text message from Kerri-Ann saying she'd left Chloe in the car and gone inside and fallen asleep.

They also tell them about Kerri-Ann exposing the girls to methamphetamines, and concerns of neglect.

"They weren't taking it as urgent," Peter says.

"I had a feeling that the girls were going to get hurt."

An investigation launched after Darcey and Chloe's deaths by the Queensland Family and Child Commission would later identify devastating failures in the department's handling of Peter's reports.

Investigators would discover that child safety's intake and assessment team discredited these reports as a custody dispute.

The department had focused on Peter's perceived motivation instead of the safety of the girls.

When the ABC tells Peter this, he is shocked and angry.

"I think someone's got a lot of questions to answer," he says.

"That's another big pill to swallow.

"Stuff-ups are bound to happen, we're all human, but to write someone off the way I was … that's unfair."

Darcey and Chloe's last day

It's Saturday, November 23, and Peter has just returned from his regular trucking trip to north Queensland.

He's been left waiting for a buyer for his car, but he's just heard that he's not going to show.

It's after 1pm and over 30 degrees.

As he walks back to his car from the shops, his phone rings. It's Kerri-Ann with the worst news possible.

When he runs into the bathroom, he finds Darcey laying there, unmoving, her skin "a yellowy, pale colour" and her lips "a purply, grey, black colour".

Peter drops to his knees and sees Chloe out of the corner of his eye.

She's also in the bathroom and looks the same.

He starts performing CPR on Darcey.

Over the phone, the operator is instructing Kerri-Ann on what to do with Chloe.

Within minutes a paramedic bursts into the bathroom, shoving Peter out of the way.

"Oh, fuck," the paramedic says as he takes Darcey.

As Peter starts trying to revive Chloe, another paramedic enters and takes her.

It's just Kerri-Ann and Peter left in the bathroom.

As Kerri-Ann turns off the tap, Peter asks her how long the kids were in the car.

"She told me an hour. I'm glad she lied," he says.

Peter and Kerri-Ann go outside.

A neighbour sees Kerri-Ann sitting on the front step, saying, "Where are they taking my babies? Where are they taking my babies?"

Peter's head is spinning.

A paramedic walks over and tells him the girls are dead.

"I just, I fell apart."

"And at that moment, I felt like I was the only person on the planet."

The what-ifs

As he is interviewed by police, Peter asks the detectives whether he could have saved the girls if he hadn't waited for the buyer of his car to arrive.

The detective shows him snippets of footage from a CCTV camera at Kerri-Ann's house, revealing the kids had been in the car since 4:10am, when the camera captured her walking inside alone.

"So it wouldn't have made a difference whether I got there at 10 because it was already 30-odd degrees at 8 in the morning," he says.

He's told it would have been above 60 degrees inside the car.

Kerri-Ann is charged with two counts of murder with reckless indifference to human life. These would later be downgraded to double manslaughter – domestic violence.

Peter attended her sentencing hearing this week, where the court heard that Kerri-Ann was awake until at least 5:55am, when she sent a text message.

The girls had been in the car for almost two hours by that time. After that, she fell asleep.

The court also heard that Kerri-Ann disposed of evidence of drug use in a bin outside her house after she brought Darcey and Chloe inside, and before she called Peter.

Peter still thinks about how the girls might be alive today under a different chain of events, but these days, his "what-ifs" are different.

What if child safety had acted swiftly on the warnings from him and others about the girls being at risk in their mother's care: could the department have prevented Darcey and Chloe's deaths?

Peter blames Kerri-Ann but says child safety is also responsible.

"They're not here. They failed them. They haven't just failed Chloe and Darcey, there are other kids there," he says.

"They're supposed to be a backup to protect these kids. But if the backup's failing, what happens then? Are we just going to watch them all die? That's wrong."

What went wrong

To examine the child protection system's handling of the girls' case, Premier Annastacia Palaszczuk ordered an investigation by the Queensland Family and Child Commission (QFCC).

The review doesn't make findings against individuals but makes recommendations on how to fix the system.

This is the first time any of the commission's findings have been made public.

The QFCC investigators found that when Darcey was first returned to Kerri-Ann in December 2017, child safety missed a crucial opportunity to work with her while she was clean by not developing a case plan.

They also found that the department closed Kerri-Ann's case too quickly when she refused to renew her agreement with child safety in July 2018.