Somewhere in a hobby shop in Denmark, a set of rotors was destined to a life of violence.

Attached to a model plane, or perhaps a quadcopter, this drone likely waited on a shelf, perhaps for months, to see if its new owners would take it on hikes, or for family photos, or maybe even film some kayaking from above. Instead, the drone was intended for service as either an insurgent scout or weapon. It never made it, because on Sept. 26, police in Denmark arrested two people on suspicion of buying drones bound for the Islamic State.

We know little more about this exact case. It was part of an ongoing investigation, and the suspects were specifically arrested under Denmark’s anti-terror laws. We do know considerably more about the flow of drones from Europe to ISIS, however, thanks to diligent work by arms investigators and trackers.

In July, the Combating Terrorism Center at West Point released a report on the Islamic State’s drone supply line. One notable component of the supply chain was a range of IT and web service companies, all named variations on IBACs, run by a pair of Bangladeshi brothers named Siful Haque Sujan and Ataul Haque Sujan. When these brothers joined the Islamic State, the Center reports, they converted their companies to fronts to supply money and material to ISIS. The companies run by the brothers operated in the United Kingdom, Bangladesh and Spain, as well as having business activity in Australia, the United States and, notably for the news this week, Denmark.

The actual workings of the network are somewhat complex, and of the two brothers at the center of it, Siful is dead and Atual is in custody. The Center found evidence that their organization acquired drones in Spain, the United Kingdom and Denmark to send to ISIS. The drone purchaser in Denmark, an unmanned 28 year old, was in custody at the time of the report’s publication. Before the network was busted, it sent drones to Sanliurfa, Turkey, which was an hour’s drive from ISIS-controlled territory.

Denmark, and this network, were not the only ways drones moved from the commercial market and into ISIS hands. In February 2018, the Treasury Department sanctioned the Turkish company Profesyoneller Elektronik for supplying at least $500,000 worth of drone components to ISIS. Other investigations found drone parts, like gyroscopes, traced back to online Turkish distributors for hobby supplies.

If there are suppliers that can acquire the drones much closer, why might people looking to get the flying robots to ISIS try to buy them in Europe instead?

“It would mean the purchaser could avoid suspicion, and potentially ‘activate’ it [as DJI products have to do] in an acceptable country before being sent to Syria,” suggests Nick Waters, an open-source analyst at Bellingcat.

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“However, there are indications that IS was getting round this ‘activation’ step by spoofing the drone’s location.”

Commercial off-the-shelf drones may also be the most valuable military equipment that can be easily acquired in Western Europe for ISIS. An investigation into the arms and ammunition flows into ISIS by Conflict Armament Research found that the overwhelming majority of weapons and ammunition were Warsaw Pact calibres, like that originally made for China, Russia and Eastern European countries. While nearly 30 percent of weapons recovered from ISIS were made by EU members, those weapons overwhelmingly came from former Warsaw Pact members, and matched the calibers of the weapons and ammunition on hand.

We will have to wait for more news from Denmark to see if these drone purchases and arrests are linked to the previous ring of drone buyers. It could represent a continuation of the tactic through different proxies, or it could be an attempt to develop new attacks for the drones, now that ISIS is in a very different position than it was when it first started acquiring drones.

However the drones are used, something rotten was bought in the state of Denmark.