Police in Calgary, Canada, have released CCTV images of four individuals wanted for a string of Bitcoin ATM thefts that amount to almost $200,000. 

The crimes involved using Bitcoin ATM’s in seven different Canadian regions to commit 112 fraudulent transactions. The majority of the transactions were made in Calgary, with several others in Toronto, Montreal, Ottawa, Hamilton, Winnipeg, and Sherwood Park. It is alleged that the crimes took place between September 16th and 26th, 2018 and that Calgary Police received information about the crimes the following month in October.

Investigators are of the opinion that the hackers were somehow able to remotely cancel Bitcoin transactions before they were processed but after physical cash had been dispensed from the ATM’s. Toronto police described the suspects as men presumably with in-depth knowledge of Bitcoin, cryptocurrencies and/or blockchain technology.

Photographs of the suspects appear to have been captured on hidden cameras inside the ATMs and possibly on in-store CCTV cameras. In the images, two men appear to be communicating via cell phone handsfree kits and looking down at illuminated devices, possibly laptops or phones.

Double-spend attacks are common in the cryptocurrency sector but are more often associated with hacks on crypto exchanges and don’t usually involve fiat cash or any physical devices. In most double-spend attacks, hackers will generate cryptocurrency out of thin air by fabricating a fake duplicate of a blockchain. This is only possible if the hackers can control over 51 percent of the hashing power and therefore are able to create blocks faster than the original chain.