An unknown individual has threatened to place bombs in the schools and churches of 18 Japanese prefectures until a Bitcoin ransom is paid out.

As per a report by local news outlet Japan Today, the emails first started back in July and have continued ever since, with the perpetrators still at large despite police efforts.

One such instance saw the email threat demanding 40 BTC, valued at over $450,000 at current prices, to the town of Yamagata in Northern Japan. Meanwhile, on the Japanese island of Miyakojima, the bomb threats were sent to elementary and junior high school and city halls.

The Yamadera town in Yamagata prefecture. Image: Shutterstock.

Such targets show a pattern. All reported mails have gone out to small Japanese towns and rural areas like Sanjo, Niigata, Tara, and Minami, ahead of big cities like Tokyo or Osaka.

That has, in turn, led authorities to question the emailer’s motives—that of the criminals trying to extort Bitcoin from municipal facilities in rural Japan where the digital currency is unlikely to be widely used or even known.

“Asahi City Hall was also threatened for Bitcoin, but they don’t have any Bitcoin in the first place,” said one local observer, the report noted.

So far, no actual bombing has ever taken place. But the emails keep coming.