Dallas police 'all clear' after high alert response to possible threat

The Associated Press contributed to this report.

Dallas police worked to secure headquarters Saturday after receiving a credible threat from a Houston group that claimed to be armed.

Police issued an all clear shortly before 9 p.m.

"The search has concluded," Dallas police tweeted. "Out of an abundance of caution, officers searched the garage to ensure reports of a suspicious person was thoroughly investigated."

The threat comes on the heels of a gunman shooting 12 officers, five fatally, in downtown Dallas.

Read more about Dallas shootings

The department was on high alert and officers initiated a citywide roll call to make sure others are OK, according to WFAA. At least two buildings were blocked off as officers stood guard wearing helmets carrying rifles outside.

There have been no shots fired as officers search a nearby parking garage, according to Dallas police. A SWAT team set off a device to enter a locked fence, officials said. Officers plan to break a locked door in the parking garage in search of a suspicious person.

The first second and third floors of the garage were cleared and employees were allowed to access their vehicles to leave, according to Dallas police.

"Officers have completed manual search of the garage. No susect found," Dallas police tweeted. "As a precautionary measure, K9 is conducting a secondary search."

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Maj. Thomas Castro told The Associated Press several general threats have been made against Dallas police, though nothing specific. A spokeswoman said the department received an anonymous threat against law enforcement across the city and has tightened security.

This is a developing story, check back for updates.