A Houston police officer, under investigation for being among the thousands who stormed the U.S. Capitol last week, has been put on leave, officials said Wednesday. 

Police Chief Art Acevado said the officer -- an 18-year veteran -- will face a disciplinary review Friday. Acevado said he received a complaint Sunday that a Houston officer may have been in Washington for the protest Wednesday against President-elect Joe Biden's Electoral College victory, "which is their First Amendment right."

But Acevedo said after he contacted the FBI, a joint investigation was launched, which determined the officer also stormed into the Capitol during the Jan. 6 insurrection.  

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"This individual has been determined to actually have ... penetrated the Capitol," Acevedo told reporters. "There is no excuse for criminal activity, especially from a police officer."

Investigators believed the officer traveled to Washington alone. He has no previous disciplinary issues, the chief said.

Acevedo did not identify the employee, but in an interview with the Houston Chronicle, Tam Pham confirmed he was the officer. He declined to say whether he entered the Capitol.

"A lot of stuff happened that day," Pham told the newspaper. "I wasn’t in the right mind."

Calls to Pham were not returned. 

Acevedo said a resident emailed him a photo Sunday night showing the officer draped in a pro-Trump flag in Washington. The chief said he went on the officer's Facebook page and confirmed it was indeed a Houston police officer. 

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"I can't tell you the anger I feel at the thought of a police officer and other police officers thinking they get to go storm the Capitol," Acevedo said. 

He is "highly confident" the officer will face federal charges. 

Calls to the Houston Police officer's union were not immediately returned. Union head Doug Griffith told the Chronicle that he expects the officer to resign Thursday. 

"I'm very disappointed," Griffith said. "If the allegations are true, he deserves to be penalized just like any other person would be. It's a crime. It was a crime to enter the Capitol — he needs to face punishment for that."

Acevedo said he would be surprised if the officer attends the disciplinary hearing.

"He has a date with me on Friday. We'll see if he shows up," he said. 

He declined to release more details, citing the ongoing investigation. 

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Several law enforcement agencies -- including in Las Vegas, New York City and Maryland -- have launched investigations after being notified about personnel possibly participating in the riot.