Police found 10-year-old Jessica Ridgeway's body. Then came the chilling 911 call.

It was the phone call no parent ever wants to have to make.

On 5 October 2012, Sarah Ridgeway dialled 911 and told the operator that her 10-year-old daughter Jessica was missing.

Jessica – a bespectacled, smiling blonde – was very independent for her age, her mother said. She had her own alarm clock and liked to get up by herself to get ready for school. She’d peel the oranges for her morning snack, eat her granola bar, and fill up her water bottle.

“She wants to make herself look like a grown up,” Sarah told podcast Sword and Scale. “She wants to be a teenager before she’s a teenager.”

That morning, after doing those things, Jessica kissed her mum goodbye and headed out into the snow at 8.35am. She was wearing blue jeans, black boots, a black puffy jacket, and her pink and purple glasses. She started out towards the nearby park where she always met the friend she walked to school with.

But on that day, Jessica did not arrive at Witt Elementary School in the tree-lined suburban town of Westminster, Colorado. She never even showed up to meet her friend.

Teachers left a message with Sarah, letting her know Jessica hadn’t arrived. But Sarah, who worked nights was asleep, delaying that 911 call by several crucial hours.

When she eventually woke up it was 4.30pm. She reported Jessica missing and the FBI began an extensive search.

They knocked on doors, blocked off roads, and urged members of the public to report anything suspicious. An army of 800 volunteers scaled hills and scoured trails nears Jessica’s home.

Two days into the search, they discovered Jessica’s backpack and water bottle 9km away from her home. Then, three days after that, a far grislier discovery: a torso, wrapped in a black plastic bag, dumped in a field.

It was Jessica’s. Where the rest of her body was, nobody knew. Or rather, only one person did.

Holly Wainwright and The Stephens Twins explore our fascination with the True Crime genre. Is it simply our love of a good story, or something more sinister? Post continues after audio.

“There is a predator at large in our community,” a police officer said in a press conference.

The police had ruled out the family and they didn’t have any other leads. The residents of Westminster – especially those with children – were terrified. Who could do this to an innocent, 10-year-old girl? Was there really evil lurking right on their doorsteps?

Then, on 19 October, a woman called the police tip line to say she had recognised a small wooden cross seen in a news report that had been found at the crime scene. It belonged to her neighbour, a 17-year-old boy named Austin Sigg. The woman said she was concerned about Sigg because he had dropped out of high school and was obsessed with death.

Police brought him in that day. They took a DNA sample, just as they had with many other locals, then they let him go home.

But a few days later, a 911 call came in. It was Mindy Sigg, Austin Sigg’s mother.

She asked if officers could come to her house. “My son wants to turn himself in for the Jessica Ridgeway murder,” she told the operator.

She said Austin had confessed, given her details, and that Jessica’s remains were in her house.

Then Austin came on the phone. When the 911 operator asked him what was going on, how he was feeling, his response was chilling.

“I don’t exactly get why you’re asking me these questions,” Sigg said calmly. “I murdered Jessica Ridgeway, I have proof that I did it, there is no other question, you should have to send squad cars, something down here and I will answer all the questions that you want to ask or anyone wants to ask of me as soon as you just – you gotta get down here.

“I’m giving myself up completely, there will be no resistance whatsoever.”

Officers rushed to Sigg’s home and arrested him. Only later would they discover just how profoundly disturbed and depraved he was.

Age 12, Sigg’s mother had caught him watching child pornography and he’d been sent to therapy. But by his own admission the sessions had not helped and his addiction to viewing such material had grown over the years.

Austin Sigg was also obsessed with death – and was even studying at college to become a mortician. He had, it transpired, been wanting to commit murder for some time.

Austin Sigg was obsessed with death and had wanted to kill for some time. Image: Getty 

Four months before he killed Jessica, he'd made his first attempt.

He'd grabbed a woman who was out jogging at nearby Ketner Lake and had shoved a chloroform soaked rag under her nose. The woman had managed to escape and call authorities.

From there Sigg knew his target had to be smaller, easier to overpower.

And that sealed Jessica's fate.

In a taped police interview, Sigg told detectives he was out "hunting" on the day he killed the 10-year-old. He described sitting in his car, watching Jessica walking alone in the snow and throwing snowballs.

He sprang from his gold Jeep, grabbed her and hauled her into the back seat. He bound her hands and feet with zip ties. It was later revealed he had practised this particular move on his own mother.

He told police: "The second I pulled her into my car, I knew she was dead."

When asked if he knew Jessica, Sigg said no, that the attack was "random place, random time, random everything."

Sigg drove for around half an hour with Jessica struggling and screaming in the back of his car.

He took her to his mother's home. There, he kept her in his bedroom for nearly two hours. He cut her hair, sat her in front of a movie. He gave her clean clothes to change into as she had soiled her own.

Then he sexually assaulted and strangled her.

He told police that when he looked at her body afterwards, all we could think was "oh god, what have I done."

Sigg dismembered Jessica's body in the bath tub and initially hid her remains behind the pool shed in the backyard. He dumped Jessica's backpack where he did to lead investigators away from his house. Days after that, he dumped the torso where it had later been found.

Sigg had suffered a panic attack at college the day after giving police a DNA sample, believing it would link him to Jessica's murder. He left school immediately and that night he told his mum everything.

Shockingly, a mistake at the testing lab had actually cleared Sigg - without his confession, he never would have been charged with Jessica's murder.

But he was - and he pleaded guilty. He also pleaded guilty to charges related to the attack on the jogger.

Because Sigg was three months short of his 18th birthday when he killed Jessica, he was not eligible for the death penalty. Instead he was sentenced to life in prison plus 86 years.

"Evil is apparently real," Judge Stephen Munsinger said.

While no sentence will bring Jessica back, there is a ray of hope for her family. Last year, Sarah Ridgeway gave birth to a baby girl, Anna. She told 9News.com that while Jessica is ever present in her life, she won't let it affect how she raises Anna.

"She definitely has an extra special angel watching over her," she said.