Two letter bombs exploded in the Netherlands on Wednesday and an anonymous criminal is asking for a Bitcoin payment to prevent future attacks, Dutch police say.

The first bomb went off at a postal sorting office in ABN Amro bank in Amsterdam on Wednesday morning. The letter bomb exploded moments after a mailroom worker tossed away the package. “The colleague who was sorting the mail heard a hissing sound, and threw the package away,” Mr. van der Varst said.

The second explosion came less than an hour later in a border town called Kerkrade. The package was mailed to a local business, the Japanese electronics firm Ricoh.

Nobody was injured in either explosion, but police say the bombs were sent along with notes demanding payment in Bitcoin to prevent further bombings.

Police have started their investigation but have not officially linked the cases together. Amsterdam police spokeswoman Lex van Liebergen said today to Dutch site De Telegraaf: “It’s fair to say that all of these are connected because the same demand was made[...] But we still don’t know who sent it. We are still investigating.”

The police have not yet revealed how much Bitcoin the unknown bomber is demanding.

This isn’t the first time the Netherlands has seen bad guys demand crypto payments. The 2015 Jumbo bomber, who put explosives in Jumbo supermarkets around the country, also demanded payoff in Bitcoin.