The 21-year-old nursing home assistant suspected of killing an elderly patient with insulin may have committed two more murders, the public prosecution department said on Thursday.

The man, who comes from Rotterdam and has worked at several nursing homes in the region, was arrested two weeks ago. The public prosecutor says he is now suspected of killing two more elderly patients. Four other suspicious deaths are under investigation as are six cases in which the patient survived.

The 12 new cases were reported by two nursing homes in Ridderkerk and one in Rotterdam.

The investigation began earlier this month after a woman at a nursing home in Binnenmaas became unexpectedly unwell. She was taken to hospital, where medical staff said they suspected she had been given a dose of insulin. Nursing home officials then called in the police.

She survived the incident but investigators identified two other suspicious incidents involving the suspect. In one case, at the same nursing home in Binnenmaas, a nursing home resident died. In the other case, in Rotterdam, a female patient also became unwell.

The man was remanded in custody for 90 days while the investigation continues.