Tokyo Metropolitan Police Department Homicide Division

The Tokyo Metropolitan Police Department Homicide Division is the investigative unit at the center of the murder inquiry in Tokyo. Its work joins methodical evidence gathering to a widening network of local and regional cooperation: investigators first identify victims and pursue leads, then test whether apparently separate people and identities belong to the same hidden history.

Role in the Investigation

The Division’s investigators confront a case in which both the woman found dead in Mutsuo Koshikawa’s apartment and Koshikawa himself initially resist identification. The apartment contains no useful identity documents or personal records, and investigators suspect that belongings may have been deliberately removed. They collect a toothbrush, safety razor, and old towel for DNA comparison, while circulating the dead woman’s physical description and photographs to police departments nationwide. The returned information produces no match, so the task force turns to fingerprints and DNA to identify her.

After the Oshitanis confirm the woman’s identity as Michiko Oshitani, Squad Leader Kobayashi and Unit Chief Ishigaki direct the inquiry toward her past. They assign Shuhei Matsumiya and Sakagami to travel to Shiga Prefecture, visit Oshitani’s former workplace, and investigate her friendships, relationships, and possible connections to Tokyo. The order illustrates the Division’s chain of command and the way a local lead becomes a task-force assignment: investigators are expected to report discoveries promptly, with additional personnel available if needed.

Evidence and Identification

The investigation depends on assembling evidence with different strengths and limitations. A witness’s response to an artist’s sketch helps the detectives connect Koshikawa to the name Shunichi Watabe. Rather than relying only on facial detail, the witness describes the impression conveyed by the sketch; the investigators regard that response as useful because a hand-drawn likeness can preserve subjective qualities that a mechanically detailed composite may fail to evoke. The testimony gives the team a working identity, not yet the final objective proof.

That proof comes from fingerprints on a train timetable preserved among Kyoichiro Kaga’s mother’s effects. Forensics finds several prints matching those recovered from Koshikawa’s apartment, and their number and placement suggest that Watabe, rather than Kaga’s mother, handled the timetable most often. The Division treats the match as objective evidence that Koshikawa and Watabe were the same person. At the same time, the inquiry considers the possibility that even apparently personal DNA sources could have been switched, keeping the provenance of evidence open to scrutiny.

Interagency Cooperation and Expanding Leads

The Division’s work extends beyond Tokyo. Shiga Prefectural Police are asked to search for a missing man who might have known both Oshitani and Hiromi Asai. Their checks identify Seizo Naemura, Oshitani and Asai’s former junior-high homeroom teacher, as the only missing person of an appropriate age found in their search. His residence registration had been canceled by the authorities fifteen years earlier, prompting Matsumiya and Sakagami to go to Shiga and follow the lead in person.

The inquiry also crosses institutional and personal boundaries through Kaga, a detective assigned to Nihonbashi Precinct who assists the task force. His investigation into his mother’s effects supplies the timetable evidence and a note listing bridge names and months, which corresponds to a calendar found in Koshikawa’s apartment. His involvement shows how information from outside the Division’s own chain of command can become central to its case, while still requiring formal cooperation and forensic verification.

From Leads to a Revised Theory

As the evidence accumulates, the task force revises its assumptions. The initial search focuses on Naemura as a possible link between Oshitani and Asai, but testimony establishes that he is not the man identified as Watabe. Kaga then proposes a different explanation: Watabe’s long connection to Asai, his limited relationships with others, and the possibility that Asai supported him financially point toward a close family bond. He argues that Watabe may have been Asai’s father, Tadao Asai.

The proposed identification also forces the investigators to reconsider the recorded account of Tadao Asai’s death. The reported suicide appears only in the files of Biwa Gakuen Orphanage and lacks supporting official records; former classmates also do not remember the supposed death. Kaga therefore reasons that the death may have taken place elsewhere and that the dead person may not have been Tadao. The Division’s investigation moves from identifying an unknown victim to questioning whether a presumed death concealed a living person’s identity. Its progress depends not on a single revelation but on connecting independent traces, challenging weak records, and treating a persuasive theory as something to be tested against evidence.