DALLAS (CBSDFW.COM) – Five envelopes containing white powder were found at Dallas-area locations Monday.

Four of the envelopes were found at schools.  The fifth was found at the Texas Instruments plant in North Dallas.

The school envelopes were found at Sunset High School in Dallas, Gulledge Elementary in Plano, Wylie High School in Wylie, and Whitt Elementary, which is a Wylie ISD school in Sachse.

Hazardous materials teams determined the white powder in the envelopes sent to the schools was cornstarch.

Crews have not yet identified the powder in the envelope at Texas Instruments.

Postal inspectors and the FBI are investigating each case, an FBI spokesman said.

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