An overdose of stimulant drugs killed a wealthy man who called himself "Don Juan" in western Japan in May, but it remains a mystery how it occurred, police said Wednesday.

Police in Wakayama Prefecture, who have been investigating the sudden death of Kosuke Nozaki, 77, as a possible murder, concluded his May 24 death was caused by acute stimulant intoxication, but there were no track marks or external injuries on his body.

The police believe it is unlikely there was an intruder at his home in Tanabe when he died, estimated to have occurred at around 9 p.m.

(Nozaki's memoirs "Don Juan of Kishu")

He was found collapsed an hour and a half later on the sofa of his bedroom by his wife of three months, who is 55 years his junior. A housekeeper was also at his home at the time.

The police have searched the home and related locations in Tokyo and have collected urine samples from people close to him.

Nozaki, president of a liquor sales company and a real estate business, was featured in TV programs and magazines after publishing his autobiography in 2016, titled "Don Juan of Kishu: The Man Who Gave 3 Billion Yen to 4,000 Beautiful Women," likening himself to the mythical Spanish playboy. The book became a best-seller.

He published a second memoir in April this year after his marriage to his current wife in February, when she was 21.