WARREN, Ohio - A Warren man has been arrested after drug agents used GPS tracking and invisible dye to trace a package that once contained a brick of a synthetic opioid.

Twenty-year-old Robert Lang is being held in the Mahoning County Jail after federal authorities charged him with Attempted Possession with Intent to Distribute a Controlled Substance.

According to an affidavit filed in U.S. District Court, a security official from FedEx notified a Home Security Special Agent on Wednesday after opening a package containing toys, kinetic sand, a bag of peanuts, and a one-kilogram, shrink-wrapped brick wrapped in a towel.

According to the FedEx Terms and Conditions posted on its website, FedEx reserves the right to open and inspect any package.

An agent from the Drug Enforcement Agency said in the affidavit that the brick tested positive for the synthetic opioid, hexanoyl fentanyl hydrochloride.

The DEA says it replaced the narcotic brick with a harmless substance, spraying it with “clue spray”, a liquid that is invisible until it is exposed to ultraviolet light.

After placing a GPS tracker in the package and a device that would send a signal when it was opened, the parcel was delivered to its intended destination, a home on Clearwater Street NW in Warren.

Keeping the home under surveillance, agents say Lang picked up the package and while driving it to another home on Stephens Avenue NW, investigators got an alert that the package had been opened.

Agents called Lang out of the home and found the empty delivery box in a trash can.  In addition, according to agents, Lang’s hands glowed green under ultraviolet light from the clue spray.

The affidavit says that under questioning, Lang admitted receiving packages containing narcotics from the same sender three times before.

Lang appeared before a Magistrate Judge in U.S. District Court on Thursday where a public defender was appointed to represent him.

Another hearing is scheduled next week to determine if Lang will remain in custody while his case proceeds through court.