5 of the most baffling unsolved cases of the past decade.

As the decade now fades, questions that surround unsolved crimes that occurred on Australian soil in the past 10 years continue to endure.

From those people who simply vanished to those who were found brutally murdered, the following cases all have one thing in common: no one can decipher what happened.

No arrests have been made, and no answers have been given. Police remain seemingly stumped.

Here are just five of the unsolved crimes that stay burned in the minds of local communities.

Theo Hayez – 2019

The disappearance of Belgian backpacker Theo Hayez has baffled the Byron Bay community and police alike.

On May 31, 2019, the 18-year-old left Cheeky Monkey’s nightclub in Byron Bay. Just after midnight, as he made his way back to his hostel, Hayez messaged a friend back home in Belgium.

Almost a week later he was reported missing when he failed to check out from the WakeUp! hostel in Byron Bay, leaving his belongings – including his passport – untouched in his room.

For months following Hayez’s disappearance, State Emergency Service volunteers, dogs, drones and members of the public searched for the backpacker. They found few clues.

In September, the official police search was brought to an end and the case was referred to the NSW coroner.

For more true crime content, listen to Mamamia's True Crime Conversations podcast. The trailer below shows what you can expect from it.

Toyah Cordingley - 2018

On Sunday October 21, 2018, Toyah Cordingley - a pharmacy worker - drove 40km to Wangetti Beach, north of Cairns, Queensland. She was with her much-loved dog, Indie.

Between 2pm and 2:30om, the 24-year-old left her Mitsubishi Lancer in the car park and went for a walk along the sand.

When Toyah failed to return home that night, her boyfriend Marco Heidenreich raised the alarm. Armed with torches, Toyah's family began searching when they found her dog tied up at the beach, alone in the dark.

Bolstered by police and SES volunteers, the search continued through to the following morning. At 7.45am, Toyah's father, Troy Cordingley, discovered his daughter's body in the sand.

"Toyah is my only child. Finding her body has burnt an indelible image in my mind," Troy wrote in a Facebook post that December. "It is something a father should never have to suffer."

In June this year, Queensland Police said that Operation Quebec Clarify – a dedicated team of detectives and support personnel – was still working on the case. At that time, they'd taken more than 400 statements and followed up over 2800 lines of inquiry.

But still no answers.

"We remain with an unwavering commitment to deliver justice for Toyah, her family, her partner, friends and the local community," Detective Inspector Sonia Smith said on the one-year anniversary of Toyah's death.

Nicole Cartwright - 2018

At 7:30am, on October 3, 2018, NSW Police were called to the affluent Sydney suburb of Hunter’s Hill after the body of a woman was found in Buffalo Creek Reserve.

It was seven days before her name was made public: Nicole Cartwright, aged 32.

Nicole was found wrapped in an orange bed sheet and covered in leaves. Her body was beaten, her head injured and her hands bound.

According to a Facebook post written by Nicole's sister-in-law, Jackie Cartwright, the 32-year-old deleted her social media accounts prior to her disappearance.

"Over the course of the last year investigators have explored numerous avenues of inquiry, spoken to many people. We have trawled through volumes of CCTV, all to try to get to the bottom of what happened to Nicole," Detective Superintendent Jason Dickinson said on the anniversary of Nicole's death in October this year.

Nicole's brother, Ben, said in a statement on behalf of the family: "We believe someone in the community knows something... Please help us find justice for Nicole."

William Tyrrell - 2014

William Tyrrell went missing on the 12th of September, 2014. He was last seen playing in the garden of his foster grandmother’s home in the small New South Wales mid-north coast town of Kendall.

That Friday morning, at around 10:30am, the cries "William, William" began echoing through Benaroon Drive, a quiet street in Kendall.

Five years later, those cries for the three-year-old boy have never stopped, as exactly what happened to the little boy remains unsolved.

In August this year, a coronial inquest took place as it investigated the key theories at the centre of the disappearance.

Counsel Assisting Gerald Craddock SC said William was likely taken by a car, before adding that police remain confident they can solve the case.

"The offender is a sneaky, complex offender who has hidden their desires for some time and has chosen to act on those desires," he said.

Listen: What Happened To William Tyrrell? Mia Freedman talks to journalist Caroline Overington about the disappearance of the little boy in the spiderman suit. Post continues below.

Siriyakorn (Bung) Siriboon - 2011

On the morning of June 2, 2011, Siriyakorn Siriboon - known as Bung to her family and friends - left her east Melbourne home to make the 10-minute walk to her school.

But as the teacher called the roll that morning, Bung was absent. The teachers presumed Bung was sick.

By about 4pm, Bung's parents began to wonder where their daughter was.

Soon after, their phone rang. It was Bung's friend Dyamai, wanting to tell her about something that was planned for school the next day.

This was how Bung's parents learned that she had not made it to class.

It has now been eight years that Bung has been missing. The police door-knocked more than 1000 doors to try and determine what had happened to the young teen, but in 2013 the investigative team on Bung's disappearance was shut down.

There remains a $1 million reward for information leading to the conviction for Bung's disappearance.

Anyone with information relating to any of the above crimes is encouraged to contact Crime Stoppers on 1800 333 000 or submit a report online. You can remain anonymous.

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