German police have seized playing cards laced with radioactive material from a restaurant owner in Berlin’s Marzahn-Hellersdorf district.

The investigators were searching for these cards for the past year and finally solved the case about two weeks ago. Police officials said that the restaurant owner was using these cards in a gambling scam.

According to the BBC, the investigation in this case started about one year ago when police — during a routine check — detected higher levels of radioactivity at a waste processing facility in Rüdersdorf area in Marzahn-Hellersdorf district. Further probing allowed police to recover some radioactive playing cards from one of the disposal truck owned by the waste processing facility. The investigators tracked the route of this truck, and eventually were led to a 41-year-old woman in Marzahn-Hellersdorf district. On November 16, Berlin police — along with officials from a radiation monitoring center — raided the home and restaurant of the suspect. Some other premises in the area were also searched. According to the police, they recovered 13 playing cards marked with iodine-125 from the restaurant during the raid.

Iodine-125 is a radioactive substance with a half-life of 60 days. It is mostly used in the medicine field. The substance was put on the playing cards in small amount, thus making it almost undetectable from a distance of more than a meter. Although the small amount of iodine-125 was not considered dangerous for humans (unless handled directly by someone), it still posed a little health risk to people living in that area.

Radioactive playing cards found by German police https://t.co/1bS1NFJ0GI pic.twitter.com/w2DCg8m1wl — CBC News (@CBCNews) November 28, 2017

Officials are currently interrogating the woman, and trying to gather information about her accomplices in the gambling trick, according to the Local. As the restaurant didn’t have permissions for gambling, the suspect could face a fine or a five-year term in jail or both as per German laws.

The authorities have also given orders to seal the area, which will now be cleaned by the health department staff to ensure there is no radioactivity in the area.

Investigators currently have no idea about the games in which these cards were being used, but they believe a detector concealed in players’ bodies would have helped such players recognize the radioactive cards, thus giving them an advantage over other players in the game.

In a similar incident in 2013, the French police arrested Italian gambler Stefano Ampollini and his two accomplices for marking some playing cards with an invisible ink. Investigators found that Ampollini used to wear infrared contact lenses during games to identify the cards marked with the ink. Ampollini and his accomplices were later fined and jailed by the French court.