The poison was discovered at Oguchi Hospital in Yokohoma

A suspected serial killer has been allegedly poisoning patients at a hospital in Japan.

An investigation into the death of Nobu Yakami, 88, who was admitted to Oguchi Hospital, found the poison was administered to him through his IV bag. Yakami died on 20 September.

Investigators also found small holes in the rubber plugs of 10-50 unused drip bags, which suggests that the acts were indiscriminate.

A toxic surfactant compound found in the victim’s drip bag matched a surfactant present in a disinfectant kept on the ward.

The hospital reported 48 deaths on the same floor since July, describing it as an increase but not indicating what the average number of deaths was for a similar period.

The bodies of an elderly couple that was expected to have also died from the toxin have already been cremated, which makes it difficult to investigate their deaths fully.

Police had suspected Sozo Nishikawa was also a victim of the same poisoning after he died from a similar surfactant poisoning on 18 September.

The drip bags that contained the toxin were brought to a nurse’s station from a pharmacy on 17 September, the start of a three-day holiday, which means that less workers were around to notice anything awry. Police are now investigating whether an insider at the hospital had been contaminating supplies.

Whilst mass murders and serial killing are rare in Japan, a rampant attacker killed at least 19 people in Sagamihara, just outside Tokyo earlier this year. The hospital itself had reports of one of its workers suffering from blistered lips after consuming a drink that might have been laced with bleach, whilst in the month prior, a nurse’s apron was slashed.