The federal agency that monitors worker safety has opened an investigation into the illness of a Florida U.S. postal worker who became sick after coming into contact with a mysterious package from Yemen.

A spokesman for the Occupational Safety and Health Administration confirmed Tuesday that the agency is looking into what made former postal worker Jeffrey Lill sick. Lill suffers from extreme fatigue, tremors, and liver and neurological problems consistent with toxic exposure.

The Florida Center for Investigative Reporting reported last weekend that Lill’s problems began after he handled the package in February 2011 at an Orlando distribution facility. He has said the package was leaking some sort of liquid.

The U.S. Postal Service has denied the package ever existed.

OSHA spokesman Michael Wald says the probe could take anywhere from a few weeks to a few months.

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