The Butterfly Killer: 3 Shocking Theories On Who Really Stabbed David's Wife, Eunju Kim

The cliffhanger ending of the Amazon Prime Video spy thriller Butterfly left viewers reeling, posing one of the most intense and heartbreaking mysteries of the 2025 television season. The central question—did the estranged assassin daughter, Rebecca, betray her father, David Jung, by murdering his wife, Eunju Kim?—has fueled endless speculation and debate across the internet since the finale aired. This article, updated as of December 2025, dives deep into the plot's darkest moment, analyzing the evidence for and against Rebecca, and exploring the most compelling alternative theories for who truly committed the shocking act.

The stabbing of Eunju Kim is more than just a plot device; it is the ultimate test of the fragile reconciliation between David and Rebecca. David, a former U.S. intelligence operative, had just risked everything to protect his daughter from the shadowy organization Caddis, only to find his new life shattered by violence. The killer's identity remains officially unknown, but the series provided several crucial clues that point to multiple possible culprits, each with a motive powerful enough to destroy the Jung family.

The Butterfly Series: Key Characters and The Tragic Incident

The series revolves around a complex web of espionage, family secrets, and betrayal. Understanding the key players is essential to solving the mystery of Eunju's attack.

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• David Jung (Played by Daniel Dae Kim): A former CIA operative who faked his death nine years prior to protect his daughter, Rebecca. He is the central figure trying to dismantle the Caddis network and save his family.
• Rebecca (Played by Reina Hardesty): David's daughter, who grew up believing her father was dead. She was trained as a ruthless assassin by Juno and the Caddis organization. Her relationship with David is the emotional core of the series.
• Eunju Kim: David's wife. She is a key member of a powerful South Korean shipping family, providing a seemingly stable life for David after he went into hiding. Her death is a catastrophic blow.
• Juno (Played by Piper Perabo): David's former colleague and the leader of the rogue intelligence network, Caddis. She is the primary antagonist, obsessed with controlling or eliminating David and Rebecca.
• Minhee: Eunju's younger sister, who is present during the final confrontation.

The Incident: In the Season 1 finale, after a tense confrontation with Juno, David, Rebecca, Eunju, and Minhee are together. Rebecca and Eunju leave to go to the restroom. When David follows a short time later, he finds Eunju bleeding out from a stab wound and Rebecca is gone. The knife is on the floor, and the immediate implication is that Rebecca, the trained killer, is responsible.

Theory 1: The Most Obvious Suspect—Did Rebecca Kill Eunju?

The series deliberately sets up Rebecca as the prime suspect, leveraging her identity as a ruthless, trained assassin who was actively trying to kill David earlier in the season.

Evidence Supporting the "Rebecca Did It" Theory:

• Opportunity and Absence: Rebecca was the last person seen with Eunju before the attack. Her immediate disappearance from the scene, leaving her father to find his dying wife, makes her look incredibly guilty.
• Trained Killer Instinct: Rebecca was molded by Caddis and Juno into a weapon. Despite her attempts to reconcile with David, her programming and deep-seated trauma could have been triggered, especially if Eunju said something that reminded her of David's past betrayal.
• The Dark Side: The plot establishes that Rebecca "turned to the dark side" after David faked his death. The murder could be the final manifestation of her complete break from her past and her father.

Arguments Against the "Rebecca Did It" Theory:

• Reconciliation Arc: The entire season is built on David and Rebecca's slow, painful path toward reconciliation. Killing Eunju—the innocent woman who brought David happiness—would completely negate her character arc and make her irredeemable.
• Following the Real Killer: A strong counter-theory suggests Rebecca disappeared not because she was guilty, but because she saw the real killer escaping and immediately went in pursuit to prove her innocence to David.
• The Weapon: A professional assassin like Rebecca would likely not leave the murder weapon behind, nor would she botch the job by not ensuring the victim was dead, suggesting the killer may have been less experienced or acting in haste.

Theory 2: The Mastermind's Plot—Juno and the Caddis Network

The most compelling alternative theory points the finger at the show's main antagonist, Juno, or one of her remaining operatives from the Caddis network. Juno's entire motivation is to punish David for leaving and to maintain control over Rebecca.

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Evidence Supporting the "Juno/Caddis" Theory:

• Ultimate Retribution: Juno knows how sensitive David is about his family. Killing Eunju is the most devastating way to punish David for dismantling her network and taking Rebecca back. It is a calculated move to ensure his suffering.
• Framing Rebecca: By attacking Eunju while Rebecca is present and then having an operative disappear, Juno can achieve two goals: destroy David's life and ensure Rebecca is blamed, driving a permanent wedge between father and daughter.
• The Unfinished Job: If Juno ordered the hit, she may have intended for Eunju to survive long enough to cause David pain, or the operative (perhaps someone like Oliver, who is not a "shrewd killer") may have been interrupted.

The logistics of the attack—Eunju and Rebecca being alone in a seemingly safe place—suggests the killer had to be either someone they knew or someone who could move with the precision of a trained operative, which aligns perfectly with Caddis's methods. The attack is a classic spy-thriller maneuver: a calculated personal attack designed to look like a betrayal.

Theory 3: The Dark Horse—The Kim Family's Enemies

A less explored but equally plausible theory involves the powerful family of Eunju Kim. The series established that Eunju's family runs a significant shipping business, which, in the world of international espionage and organized crime, is rarely clean.

Evidence Supporting the "Family Enemies" Theory:

• Unseen Enemies: David's world is full of enemies, but Eunju’s family background introduces a whole new layer of potential threats. The attack could be entirely unrelated to David and Rebecca's spy drama, instead being a hit stemming from a business rival or organized crime syndicate targeting Eunju's father.
• A Coincidence of Timing: The timing is suspicious, but it's possible the hit was planned long ago and only coincidentally occurred when David and Rebecca were nearby. The killer may have been surprised by Rebecca's presence, leading to the frantic, in-and-out nature of the attack.

This theory adds a layer of topical authority by introducing the theme of collateral damage—the innocent victim caught between two warring worlds. It would also set up a potential plot for a second season where David and Rebecca must hunt down a non-Caddis threat while still being hunted themselves.

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The Verdict: Who Is the Butterfly Killer?

As of the latest updates, the identity of the killer remains the central mystery of the series, designed to be the ultimate cliffhanger for Season 1. The show intentionally leaves David and the audience believing that Rebecca is the culprit, which is a classic misdirection in the spy genre.

The most likely answer, based on narrative structure and genre tropes, is that Rebecca did NOT kill Eunju. The evidence strongly suggests that Juno or a Caddis operative orchestrated the attack to frame Rebecca and inflict maximum pain on David. Rebecca’s disappearance is a calculated move to track the real killer. This twist maintains the emotional complexity of the father-daughter relationship while setting up a high-stakes, revenge-driven plot for Season 2.

The resolution will only come with the premiere of Butterfly Season 2, where David will be forced to choose between his instinct to protect his daughter and his grief-fueled desire for vengeance. The killer's true identity will not only reveal the extent of Juno's depravity but also determine whether Rebecca is truly capable of redemption.