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A Kansas police officer was fired Sunday after threatening a Dallas woman and her 5-year-old daughter on Facebook, authorities said.

The threat came after a sniper opened fire on a protest in Dallas, killing five police officers and wounding seven more.

In a statement, Overland Park Police Chief Francis Donchez Jr. said an investigation concluded that "it was obvious that our officer did not meet the standards of professionalism" at the department.

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Donchez didn't name the officer. NBC News hasn't independently verified a name being widely reported online.

The comment was posted Thursday night on a 2014 post by LaNaydra Williams, which included photos of her daughter. It read:

"We'll see how much her life matters soon. better be careful leaving your info open where she can be found :) hold her close tonight, it'll be the last time"

Overland Park, Kansas, police said this comment by a city officer does not 'represent the Overland Park Police Department in any way.'

"I felt horrified," Williams told NBC station KSHB of Kansas City, Mo.

"For this guy to just come out of nowhere, just being disrespectful, how can you be an officer? How, how?" she asked. "That's unacceptable for a police officer — for anyone, but especially for a police officer."

In the statement, Donchez said that after professional standards investigators verified the post, the officer was immediately fired.

"I want to publicly apologize to those affected by our officer's personal actions," the statement said. "His actions do not represent the Overland Park Police Department in anyway and no one should be subjected to any type of discrimination or this kind of behavior."

A criminal investigation is under way, police said.