The Breakthrough ending explained: Who is the murderer of Adnan and Gunilla?

The Breakthrough is Netflix’s Swedish crime miniseries dramatizing Sweden’s second-largest murder investigation. Directed by Lisa Siwe and based on Anna Bodin and Peter Sjölund’s non-fiction book, this four-episode thriller was released globally on January 7, 2025.

Produced by Lejla Bešić under FLX, the show stars Peter Eggers as detective John Sundin and Mattias Nordkvist as genealogist Per Skogkvist. Its innovative premise of using genealogy to solve a cold case has captivated audiences.

At its heart, The Breakthrough unravels a shocking double homicide in Linköping that had baffled investigators for 16 years. David Nilsson killed Adnan and Gunilla in Linköping. He confessed to the murders, claiming that voices in his head compelled him to commit the crime.

The plot follows detective John Sundin’s obsessive quest to solve the murders of young Adnan and Gunilla, an older woman who tried to save him. The investigation’s resolution hinges on an unexpected genealogical connection, culminating in a shocking arrest and a bittersweet conclusion. Let’s delve into how the events unfolded and the secrets that were finally uncovered.

Disclaimer: This article contains major spoilers from The Breakthrough. Reader’s discretion is advised.

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The Killer’s Identity revealed in The Breakthrough

Who is the murderer of Adnan and Gunilla in The Breakthrough (Image via Netflix)

The question of who brutally stabbed Adnan and Gunilla in Linköping is the focal point of the series, which generates tension. Detective John Sundin’s optimism was diminishing after sixteen years of unsuccessful investigations.

Nevertheless, with the assistance of genealogist Per Skogkvist, the killer was identified as David Nilsson when his DNA was a perfect match with the evidence from the crime scene. The pivotal moment occurred when Stina, a journalist, submitted her DNA sample. Skogkvist meticulously traced her lineage to two men, Stefan and David Nilsson, through genealogical mapping.

The decision to apprehend David, a socially isolated individual who matched the psychological profile of the suspect, was vindicated. David confessed, admitting that the voices in his head compelled him to kill, under the impression that it would provide him with tranquility.

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How genealogy solved the case

The groundbreaking technique that solved this case was genealogy. Per Skogkvist used DNA evidence gathered in 2004 and improved by contemporary methods in 2020. Skogkvist tracked down possible relatives of the suspect by creating family tree maps using distant DNA matches, eventually focusing on the Nilsson brothers.

There were difficulties in the police’s cooperation with Skogkvist. Procedural delays and privacy concerns nearly caused the investigation to fail. As Stina questioned whether using genealogical data was legal, her involvement created additional tension.

However, her DNA sample proved to be the link between David Nilsson and the crime. This moment was a historic application of genealogy to criminal investigations in Europe.

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David Nilsson’s motive and confession

A still from The Breakthrough (Image via Netflix)

David Nilsson’s confession was as unsettling as the murders themselves. He claimed to hear voices that instructed him to kill two people to achieve mental peace.

This psychosis-driven motive left the investigators and the victims’ families grappling with its senselessness. After his arrest, David underwent a psychiatric evaluation and was sentenced to indefinite psychiatric care. His brother Stefan’s normal life stood in stark contrast, highlighting the unpredictability of mental illness.

The aftermath brought closure to some extent. John Sundin informed Adnan and Gunilla’s families, who waited years for justice. Saad, Adnan’s father, expressed his gratitude by gifting Adnan’s watch to John, symbolizing the shared journey of grief and resolution.

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The emotional fallout

A still from the Netflix series The Breakthrough (Image via Netflix)

John Sundin’s Journey

John Sundin’s 16-year quest for justice was not without its personal toll. His obsessive commitment strained his marriage, resulting in a divorce from his wife and separation from his son, Henry.

John finally began to mend his fractured relationships after the case’s resolution, which marked a turning point. A poignant moment at a pizzeria suggested a new beginning with Henry, as the father and son collaborated on a diving excursion.

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The families’ closure

The families of the victims experienced a range of emotions in response to the resolution. Although the killer’s capture yielded answers, the insanity of the motivation caused persistent anguish. The woman who attempted to rescue Adnan was honored by Saad’s gesture of naming his youngest daughter Gunilla, which served as a poignant tribute to her courage.

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Stina’s role in the investigation

Although controversial, Stina’s role was crucial. Despite her initial skepticism of John’s methods, she unwittingly played a critical role in the case’s resolution when her DNA connected the Nilsson family tree to the perpetrator. In conclusion, the series concluded with her decision to publish a book that detailed the investigation, underscoring the pioneering role of genealogy in contemporary criminology.

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Is The Breakthrough based on a true story?

A still from the Netflix series The Breakthrough (Image via Netflix)

The Breakthrough is a dramatization of the 2004 double murder in Linköping, Sweden, and is inspired by true events. The program is derived from the book by Anna Bodin and Peter Sjölund, which explains the process of forensic genetic genealogy in resolving the case. This instance started the employment of such technology in Europe to solve murder investigations.

In 2020, 16 years after the crime, Daniel Nyqvist, the real-life killer, was apprehended. He, like his fictional counterpart, admitted to hearing voices that compelled him to commit murder and was subsequently sentenced to indefinite psychiatric care.

The show’s portrayal of genealogy as an investigative tool is reminiscent of its groundbreaking application in real-world cases, such as the Golden State Killer in the United States. Although dramatized, The Breakthrough illustrates the detectives’ unwavering commitment to justice and the transformative potential of forensic science.

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Stay tuned for more news and updates on The Breakthrough and similar projects as the new year progresses. The show is currently available to stream on Netflix.