For 16 years, the Linköping killer walked free. Then came the breakthrough nobody expected.

On the morning of October 19, 2004, a tragic and seemingly senseless act of violence shattered the tranquillity of Linköping, a small Swedish town.

Eight-year-old Mohammed Ammouri was making his way to school when a masked individual viciously attacked and fatally stabbed him.

Nearby, 56-year-old Anna-Lena Svensson witnessed the horrifying incident and courageously tried to intervene, but tragically lost her life in the process.

Watch: SBS Insight 'DNA Secrets' with Amy Tan. Post continues after video.

The randomness and brutality of the murders horrified the nation.

With no apparent connection between the victims and no clear motive, investigators were left with a puzzling and chilling case. Their only significant lead was DNA evidence from the crime scene, including the perpetrator's discarded hat.

Despite exhaustive efforts, the DNA didn't match any profiles in existing databases. Over time, the case went cold, becoming one of Sweden's most notorious unsolved crimes.

Though public attention eventually faded, Swedish detectives and the victims' families remained steadfast in their pursuit of justice.

Investigators revisited the evidence multiple times, but for years, the lack of any viable matches made progress impossible — until forensic genealogy opened new doors.

By 2020, the use of forensic genealogy had already proven effective in cases like California's Golden State Killer, Joseph James DeAngelo, decades after his crimes.

This innovative technique uses DNA samples to map family trees via public genealogical databases, enabling investigators to identify suspects by tracing connections through their relatives.

Inspired by its success abroad, Swedish authorities partnered with genealogist Peter Sjölund to apply this groundbreaking method to the Linköping murders.

Sjölund's work required meticulous analysis of the DNA recovered in 2004. He painstakingly constructed an expansive family tree spanning over 200 years, narrowing down potential suspects branch by branch. This effort eventually led investigators to the perpetrator's relatives and, finally, to the killer: Daniel Nyqvist.

At 37 years old, Nyqvist had lived much of his life under the radar, with the crime occurring when he was in his early 20s.

Upon being apprehended, he confessed almost immediately, claiming he had acted under the influence of voices in his head.

Nyqvist was subsequently sentenced to indefinite psychiatric care. Today, he reportedly remains at the Regional Clinic in Vadstena under treatment.

After 16 long years, the case that had haunted a town and two grieving families had finally been resolved.

Now, Netflix's miniseries The Breakthrough tells the story, capturing both the chilling events of 2004 and the trailblazing investigation that cracked the case in 2020. Across four episodes, the show moves between the initial aftermath of the murders and the methodical hunt for answers years later.

Actors Peter Eggers and Mattias Nordkvist play fictionalised versions of Detective Jan Egon Staaf and genealogist Peter Sjölund, representing the dedicated team that refused to give up on solving the crime.

When making the series, director Lisa Siwe aimed to emphasise the victims and detectives, rather than Nyqvist and his senseless crime.

"Though this is a fictional drama series about a crime, it is, above all, a depiction of a human tragedy — where we place our focus on the victims and the investigation rather than the perpetrator," she explained in an interview with Netflix.

While some elements of the story were adapted for dramatic purposes — names and certain timeline details were adjusted — the series remains faithful to the heart of the case, honouring both the victims and the breakthroughs.

In a genre often criticised for glorifying offenders or sensationalising violence, The Breakthrough shifts the narrative to centre on the resilience of the victims' families and the unwavering dedication of those seeking justice.

Feature Image: Netflix