Investigators are looking into the origins of a letter sent from Conyers that threatened to blow up the Twin Towers and shoot first responders, according to the Rockdale County Sheriff's Office.

RCSO Sgt. Jodi Shupe said a postal worker had noticed the letter and notified the manager on duty.

The letter reportedly threatened to "blow up the Twin Towers, a New York airport, and shoot alot of people" including first responders that come to the scene, according to RCSO reports.

The letter was traced to a drop box in the Harvest Grove Apartment Complex on May 11. The identity of the writer is under investigation.