Hamaoka Nuclear Power Station becomes a crucial point in the search for Shunichi Watabe, a man whose name may have concealed the identity of Tadao Asai. Although old employment records were scarce and the nuclear industry’s contractor networks made verification difficult, a surviving work roster identified Kazutoshi Yokoyama, whose career connected Hamaoka with Onagawa Nuclear Power Station. The station thus serves as both a workplace in the investigation’s trail and a window onto the precarious, fragmented labor system that made concealed identities possible.

A workplace recovered through old records

The investigation initially struggled to establish whether Watabe or Mutsuo Koshikawa had worked in the nuclear industry. Years had passed, and companies were generally required to keep employee documents for only three years, with the obligation applying to full-time workers rather than short-term laborers. Work was often routed through successive contractors and subcontractors; workers might be hired under false names, while small firms and incomplete records obscured who had employed them.

A lead from Hamaoka eventually offered a name investigators could check. A former subcontractor crew leader, contacted after someone at the station reached out to police, recognized a man in an investigative sketch. Old work rosters preserved by the crew leader supplied the name Kazutoshi Yokoyama. The witness had known Yokoyama only at work and could offer little about his personal life, but the roster provided a concrete connection to a crew at Hamaoka more than twenty years earlier.

From Hamaoka to Onagawa

The lead mattered because Yokoyama’s employment history extended beyond Hamaoka. Investigators learned that he had also worked at Onagawa Nuclear Power Station, where he spent more than half his career. This overlap gave the task force a way to pursue a possible connection between the two workplaces and the men whose identities were under investigation; it did not, by itself, establish that Yokoyama was Watabe or Koshikawa.

Police pursued such leads across the industry, contacting smaller power companies and asking whether they had employed either name or recognized the sketch. The effort was spread across police forces nationwide, whose investigators spoke with company bosses, crew leaders, and former workers. The task was especially difficult because, after the 2011 earthquake and tsunami, many smaller firms had left the business, further thinning the available records and witnesses.

The labor system behind the trail

The investigation’s account of nuclear-plant work explains why a station name could be easier to recover than a worker’s identity. Short-term laborers were often employed through layers of small subcontractors, and records might not preserve their work histories for long. A worker interviewed by investigators described a cycle of temporary dormitories and assignments: laborers stayed for a couple of months at one location, then moved to another plant, repeating the pattern. He said that he had worked that way for four years.

The same worker described maintenance as a struggle against contamination. His task at Mihama was to scrub affected areas with cloths and brushes. The contrast between sophisticated power-station technology and manual cleaning makes the work’s physical simplicity striking, while the broader employment structure leaves the individual worker difficult to track. The investigation also learned that radiation exposure could bring comparatively high earnings, but that intermediaries siphoned off a substantial portion of the money.

Investigative significance

Hamaoka’s importance is evidentiary rather than conclusive: a former crew leader’s recollection and preserved roster turned a vague industry-wide search into a named employment lead. Yokoyama’s later connection to Onagawa widened that lead, while the subcontracting system explained both the difficulty of verifying old employment and the possibility that a worker could circulate under an assumed name. These findings helped establish the investigative context in which Kaga reconsidered Watabe’s identity and proposed that Watabe was in fact Tadao Asai; the station records were one part of the wider chain of reasoning, not proof of that conclusion on their own.