Investigators looking into a suspected arson at an acupuncture clinic in Tokyo's Chuo Ward arrested an acupuncturist Wednesday in a separate case on suspicion of raping a woman at the clinic after drugging her.

Officers at Tsukiji Police Station said they arrested 31-year-old acupuncturist Akihito Nosaka of Tokyo's Itabashi Ward for allegedly raping the 23-year-old woman on the afternoon of Sept. 4.

Nosaka was arrested on suspicion of giving the patient a drug that made her sleepy and groggy and then raping her, investigators said.

Nosaka has admitted to the charges, according to police, who said they have already confiscated a sedative from the clinic.

He told the woman that her stomach was not well and urged her to take the drug, police quoted him as saying.

The officers were initially investigating a fire that broke out at the clinic last Friday night. One patient, Hiromi Ishigami, a 31-year-old office worker from Urayasu, Chiba Prefecture, died due to massive burns sustained in the fire.

Nosaka, who was at the clinic at the time, and a woman working in the neighborhood who rushed to the scene upon hearing the clinic's fire alarm, suffered minor burns.

Nosaka was released from the hospital earlier Wednesday, and voluntarily responded to police questioning regarding the rape, for which the unnamed woman had filed a complaint.

According to accounts by the acupuncturist, a foreign thief set fire to the clinic after stealing money, but police said they found no evidence of any break-in that would support Nosaka's claim.

They are now viewing the fire as a possible arson to camouflage a murder, further details of which were not provided, investigative sources said.