CBS Local — Inmates at a prison in Michigan received a secret mail drop that wasn’t discovered by guards for two months. The packages were reportedly dropped into the criminals’ hands by a drone hovering above the facility.

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The Michigan Department of Corrections announced on Sept. 29 that they had spotted the illegal delivery on surveillance video, per The Detroit News. They added that inmates at the Richard A. Handlon Correctional Facility were seen picking up two boxes dropped in by the high-tech smuggler. Investigators say the packages were likely carrying cellphones, which are banned in prison.

The drone drop took place at some point around May 29, according to spokesman Chris Gautz. Similar cellphones were found with inmates shortly after the incident. A third package containing phones and marijuana was intercepted by prison officials on that day.

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State Police and prison officials also announced that three men were arrested after another attempted drone drop at the same prison three months later. Those boxes reportedly had more cellphones, razor blades, and drugs in them. Patrick Corey Seaton Jr., Jonathan Larawn Roundtree, and Daryl Steven Marshall all face smuggling charges for the failed Aug. 17 incident.

“We are very concerned about drones being used for smuggling, and we have implemented … certain detection and safety precautions so that hopefully in the future any drone delivery will be detected,” said State Police Detective Sgt. Christian Clute.

State Police did not reveal the new plans to keep high-flying bandits out of their jails.