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.

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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.

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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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