A 31-year-old former nurse was arrested Saturday for allegedly murdering an elderly patient in 2016 at a Yokohama hospital where three other patients also died under suspicious circumstances, police said.

Ayumi Kuboki has admitted to killing Sozo Nishikawa, 88, who died on Sept. 18, 2016, at what was then Oguchi Hospital in Kanagawa Ward, according to the police. He was found to have been poisoned with a surfactant compound.

Kuboki told them she injected disinfectant into intravenous drip bags used to treat about 20 patients, according to investigative sources.

Traces of a surfactant compound were also found in the bodies of three other patients who died. One of them, Nobuo Yamaki, 88, died two days after Nishikawa in the same room, and the same type of toxic substance was found in his body and in an intravenous drip bag that had been used to treat him, according to police.

Kuboki has told police she repeatedly injected disinfectant into drip bags, the sources said, adding they are investigating the possibility that the nurse killed Yamaki as well.

Starting in July 2016 and continuing until Sept. 20 of the same year, 48 patients died at the hospital, including five patients on a single day in late August and four on one day in early September.

The substances found in their bodies were the same as the disinfectant used at the nurses’ station on the fourth floor of the hospital where the two men were hospitalized.

Among about 50 unused drip bags at the nurses’ station, about 10 were found to have small puncture holes in them. The police believe someone may have used a syringe to inject the disinfectant into the bags.

Soon after the deaths of the two patients, police began investigating the case as possible murders committed by someone with knowledge of the hospital and medicine.

Shortly after police began investigating the deaths, the nurse said that she was not involved in the incidents and had not noticed anything unusual at the hospital.

Before she was arrested, Kuboki flatly denied lacing IV drip bags with poisonous substances, and said she was “shocked” by the incidents and “felt very sorry for the victims as well as their families.”

Beginning about six months before Nishikawa’s death, a series of suspicious incidents occurred at the hospital. In April 2016 shredded nurses’ aprons were found, in June part of a patient’s medical records was lost, and in August a nurse tasted what she believes was bleach in a bottled drink.

According to her mother, Kuboki told her she was afraid of working at the hospital at night and wanted to quit her job.

KEYWORDS nurses, hospitals, Kanagawa