The investigation is being complicated by the fact that the bodies of the majority of the dead have already been cremated, but police increasingly suspect that the killings were carried out by a person employed at the hospital and with some medical knowledge.
The 10 drip bags that have subsequently been found to be damaged were stored behind the nurses' desk on the fourth floor of the hospital, where all the suspicious deaths happened.
On July 26, Satoshi Uematsu, a former nursing care attendant at a facility for mentally handicapped people in nearby Sagamihara, killed 19 residents with a knife and injured a further 27 patients and staff.
Uematsu, 26, told police he decided to euthanise the patients "for the benefit of society" and because his demands that the government euthanise the mentally ill had been rebuffed.