A 62-year-old man was arrested Tuesday on suspicion of attempting to blackmail major discount store chain Don Quijote Co. last year.
Tokyo police identified the suspect as Kotaro Hayasaki, a company employee from Hiratsuka, Kanagawa Prefecture.
Hayasaki allegedly sent a threatening letter to the company in September containing potassium cyanide and a note demanding 50 million yen.
According to police, he has admitted to the allegations, saying he wanted the money to pay off debts of more than 10 million yen. He was quoted as saying he got hold of the cyanide more than 20 years ago, when he was working at a metal-plating factory.
Hayasaki is also suspected of sending five other threatening letters to Don Quijote by the end of October, and phoning the firm with threats to tamper with products on store shelves unless the Tokyo-based firm coughed up 50 million yen.
Although he specified dropoff points for the money, no one came to the locations and there was no indication that Don Quijote products were tampered with, police said.
According to investigators, the first threatening note was delivered in an envelope containing roughly 1 gram of cyanide. A dose of about 0.25 gram is lethal.
The note read: "This amount is enough to kill two people. I want you to purchase the remaining 24 grams I have for 50 million yen."
Several locations were designated as money dropoff points. One was in Ebina, Kanagawa Prefecture.
Don Quijote was established in 1980 and has some 1,000 employees.
It is known for discounting a wide range of items, including food and electrical appliances, at some 75 outlets nationwide.