There was a brief scare at the Cheyenne Public Safety Center Thursday morning when a suspicious letter was discovered inside the mail room.

Cheyenne Fire Rescue says crews were called to the scene at 9:08 a.m. and arrived five minutes later.

"The package had a white powder spill from the envelope," CFR said in a joint press release. "No health threat was identified after testing occurred on the substance conducted by CFR hazardous materials technicians."

The incident remains under investigation by the Cheyenne Police Department.

See 20 Ways America Has Changed Since 9/11

For those of us who lived through 9/11, the day’s events will forever be emblazoned on our consciousnesses, a terrible tragedy we can’t, and won’t, forget. Now, two decades on, Stacker reflects back on the events of 9/11 and many of the ways the world has changed since then. Using information from news reports, government sources, and research centers, this is a list of 20 aspects of American life that were forever altered by the events of that day. From language to air travel to our handling of immigration and foreign policy, read on to see just how much life in the United States was affected by 9/11.