Police referred to prosecutors on Wednesday the case of a man suspected of murder and arson at an Osaka mental health clinic last December that resulted in the deaths of 26 people as well as the suspect, investigative sources said.

The investigation of the suspected arson on Dec. 17 has come to an end, with prosecutors expected to drop the case after the suspect, Morio Tanimoto, 61, died before police were able to question him.

Tanimoto is suspected of spraying gasoline and starting a fire at the clinic, killing 26 people, including regular visitors to the clinic and its director, Kotaro Nishizawa, 49. He is also suspected of lighting a fire at a house he was living in just before the incident.

Tanimoto had been a patient at the clinic in the Osaka's Kita Ward since 2017 and visited it a total of 112 times. He died on Dec. 30 after being taken to hospital from the clinic in a critical condition.

At the time of the incident, he had no money in his bank account and no log of phone calls with acquaintances, the sources said.

On the day of the incident, many people were visiting the clinic for a scheduled group therapy session to help individuals on leaves of absence to return to work.

Data on Tanimoto's smartphone indicated that he visited the clinic from June last year, suggesting he was checking the flow of patients and chose a day when it would be busy.