In the third episode of "The Breakthrough," titled "Family Tree," the investigation into the 2004 double murder in Linköping takes a dramatic turn as Detective John Sundin and genealogist Per Skogkvist explore the use of genealogical mapping to identify the killer. The episode delves into the complexities of using family registries and the ethical and legal challenges they face in their pursuit of justice.
The episode begins with John and Per seeking approval from their superiors to employ genealogical mapping in their investigation. The officers express concerns about privacy violations, questioning whether accessing family registries is a breach of confidentiality. John counters by citing the success of the Golden State Killer case, where similar methods were used. Reluctantly, they grant him two weeks to solve the case before it is relegated to the cold case unit.
As the work commences, Per encounters a significant obstacle: the DNA profile from 2004 is incomplete due to outdated technology. The blood on the murder weapon has been fully utilized, leaving them with an incomplete DNA profile. Despite this setback, John urges Per to proceed. Per's diligence pays off as he identifies three ancestral matches, all from Germany, with one being a resident of Linköping.
Meanwhile, John encounters Gunilla's husband, who is weary and disheartened by the lack of progress. John's impatience leads him to push Per for an international warrant to access the German registry and to make premature statements. Per, frustrated by John's pressure, initially backs out of the investigation. John's personal life is also strained as he attends an awkward meeting with his son, Henry, who is distant and aloof.
Back at the case, John's persistence pays off when the forensics team discovers a small amount of DNA on the beanie left at the crime scene. They work diligently to create a new, more complete DNA profile, giving John renewed hope. Per, who had returned to his mundane life, is approached by John, who apologizes and promises to follow Per's lead. John reveals that the case has become deeply personal to him, and Per agrees to rejoin the investigation. With the new DNA profile, Per identifies over 800 matches related to the killer, and John's team is optimistic about the breakthrough.
However, their progress is threatened when the EU's data protection laws deem Per's method illegal. John pleads with his superior, Miran, to turn a blind eye until the end of the week. Despite the official dismissal, Per manages to narrow down the search to three matches in Östergötland, believing the killer has a connection to one of them.
In a subplot, journalist Stina Eriksson returns home after her father's passing and discovers her article on John. Curious about the ongoing investigation, she learns about the genealogist's involvement and questions its legality. Meanwhile, John's colleague, Francy, advises him to balance his life and not lose himself in the case. John agrees to reconnect with his son, Henry, and leaves him a voice message.
As the deadline looms, John and Per face increasing pressure. Stina confronts John about the legality of their methods, and Miran gives them two more days to solve the case. Believing they are close to a breakthrough, John asks Stina to withhold her story in exchange for an exclusive interview.
Per's mental health begins to deteriorate, and he hallucinates, lashing out at the squad. Concerned, John takes Per jogging and shares his own story of ruining his athletic career by competing in the Olympics while injured. The episode ends with John urging Per to take a break, highlighting the emotional toll the investigation has taken on both of them.
"Family Tree" is a compelling exploration of the ethical dilemmas and personal sacrifices involved in solving a cold case. It showcases the determination of John and Per to push boundaries and the impact of their relentless pursuit on their personal lives. The episode sets the stage for the potential resolution of the case, emphasizing the importance of perseverance and the power of unconventional methods in the quest for justice.