photo28 Frank Crowley Courts Building Sent White Powder Letter

A HazMat team on-scene at the Frank Crowley Courts Building on April 9, 2012 after an employee opened a letter containing a white powder. (Credit: LP Phillips/1080 KRLD)

DALLAS (CBSDFW.COM) – A Hazardous Materials team was dispatched to the Frank Crowley Courts Building Monday morning after someone in District Judge Larry Mitchell’s office opened a letter that contained a white powder, Dallas Fire Rescue spokesman Jason Evans said.

The white powder proved to be yet another false alarm –– Dallas Fire Rescue was on scene by 10 a.m. and it was business as usual an hour later.

Investigators are testing the substance, but Evans said it was not hazardous.

In recent weeks, dozens of envelopes containing mysterious white powder have cropped up across the Dallas-Fort Worth Area. In most of the cases, the substance inside was cornstarch, Evans said.

On March 5, authorities scrambled to five locations after employees came into contact with letter powder.

Suspects mailed one to the Texas Instruments plant in North Dallas; Dallas’ Sunset High School; Plano’s Gulledge Elementary; Wylie High School in Wylie; and Whitt Elementary, a Wylie ISD school in Sachse.

A week later, a doctor’s office employee in DeSoto opened a letter containing corn starch.

The U.S. Postal Service and the FBI are investigating each case.