Kanagawa prefectural police said today they searched 31-year-old Ayumi Kuboki's apartment in Yokohama, near Tokyo, for more evidence in the case.
Local media say Kuboki told police she may have poisoned about 20 patients to have them die when she was off-duty.
Police say they arrested Kuboki on suspicion of killing two elderly male patients within days in September 2016 by injecting disinfectant into their intravenous drips at the hospital.
Police have since investigated the case. The hospital has acknowledged a spike of patients' deaths around that time.
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