DALLAS -- Federal magistrates say they hope to solve the choke of a white color competency mailing case in U.S. account because the learning are tying up first responders and costing taxpayers millions of dollars.

Amanda McMurrey of the U.S. Postal Inspection Service says magistrates believe the same someone has sent nearly 400 learning containing non-toxic pulverized substance to places across the political division and abroad from Texas over the past four years.

She says officials have found similarities in the learning and the way they were mailed, but the surmise has proved elusive in part because no touch prints have been discovered.

McMurrey says while no one has been harmed, each happening diverts fire part personnel and funds.

Investigators say two mistrustful learning reported Thursday aren't coupled to the case.

Read more: White Powder Mailing Case Costing Taxpayers Millions