WAKAYAMA—Kosuke Nozaki made no secret of his life of extravagance and womanizing.

But the death of the self-proclaimed “Don Juan” in late May has created a mystery for investigators.

An autopsy showed the cause of the 77-year-old’s death was acute simulant drug poisoning, Wakayama prefectural police said June 6.

They are now trying to determine if the company president was the victim of an accidental drug overdose or was murdered.

According to the police announcement, Nozaki’s wife found him lying in a bedroom on the second floor of his house in Tanabe, Wakayama Prefecture, around 10:30 p.m. on May 24. She called an ambulance, and a housekeeper applied cardiac massage.

However, he never recovered. The estimated time of death was 9 p.m.

His body showed no conspicuous external injuries, and the bedroom had not been ransacked.

According to investigators, the autopsy revealed a lethal dose of stimulants in his blood and stomach contents.

With no signs that the drugs had been injected into his body, police suspect the stimulants entered through Nozaki’s mouth, either voluntarily or forced.

Police are trying to determine the origin of the drugs.

On June 2, they searched his wife’s second house in Tokyo’s Shinjuku Ward. The next day, they searched the housekeeper’s home in Minato Ward in the capital.

Police are also checking video footage from security cameras installed at Nozaki’s house.

Nozaki operated businesses related to alcohol sales and real estate in Tanabe.

In 2016, he published a book that boasted of his sexual escapades with thousands of women.

The title of the book was “Kishu no Don Juan” (Don Juan of Kishu), named after the region in and around Wakayama Prefecture and the mythical Spanish playboy.

In the sequel to the book, published in April this year, Nozaki revealed that he remarried a woman in her 20s in February.

The June 6 announcement of Nozaki’s name and the cause of death was the first by prefectural police in the case.

Police normally withhold such information in deaths that have not been confirmed as murders.

However, they said they made the announcement because many media organizations have already reported his death and revealed his name. If police kept his identity anonymous, it could cause confusion, they said.

They also informed his widow that they would make the announcement.