DALLAS (CBSDFW.COM) – There have now been nine white powder scares in two days in North Texas cities.

The latest suspicious package was found at the Mi Escuelita Preschool at 4231 Maple Avenue in Dallas’ Oak Lawn neighborhood. The school is another Headstart campus, which now comprise seven of the nine targets.

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The ordeal spans a number of area cities and police departments, but on Wednesday, the Federal Bureau of Investigation is now the lead agency.

The FBI is reportedly frustrated by the number of envelopes that have popped up.

Beverly Esslebach at the Dallas FBI office said the bureau takes each one of these letters seriously and investigates each one.

“We are looking at patterns,” said Esslebach. “This is a joint investigation. It’s nationwide, bureau-wide.”

Wednesday morning an employee of the Mi Escuelita Headstart school opened the mail when something stopped her in her tracks. A white substance began to spill out of one of the envelopes.

Gayle Nave is the school’s executive director.

“The person who had opened it was very cautious,” said Nave. “She noticed it immediately and called 9-1-1.”

Employees at Mi Escuelita say the envelope was correctly addressed to the Headstart but did not have a return address on it.

Dallas Police secured the scene while Plano’s HAZMAT team was called in to handle the envelope filled with a white powdery substance.

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Officials evacuated only the building where the envelope was opened, but that included one classroom with 18 children.

School officials didn’t have another classroom available for those students so they were all sent home.

Parents, like Betty Prado, received a phone call to pick up their children.

“It’s scary,” said Prado. “I need to pick up my child right away that’s scary to hear stuff like that.”

This now makes the seventh Headstart school in two days targeted with these envelopes containing a “white powdery” substance.

Tuesday, schools in Mesquite, Garland and Irving received similar suspicious mailings. Two other locations, including a church, also received envelopes.

All of them were determined to be non-hazardous.

The employee who opened the envelope was taken to a hospital and quarantined until she was cleared. She returned to work just hours later.

Meanwhile parents and administrators say they hope authorities can figure out who is behind all of this, soon.

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“It’s disturbing to me,” said Nave. “Our children are so precious. We’re so careful and we’re so safe with our kids. It just upsets me that someone thinks this is funny.”