Dallas police officers and SWAT units combed a parking garage adjacent to the department’s downtown headquarters Saturday after a suspicious person was seen on the garage’s second floor.

Authorities confirmed to Fox News that the person was spotted in an area of the garage reserved for police officers and employees and ran away when confronted. Approximately two hours after the original sighting, a search of the garage turned up no suspicious person or object.

Shortly after the search began, Dallas police confirmed that they had “received an anonymous threat against law enforcement across the city” and had taken “precautionary measures” to heighten security.

The parking garage incident highlighted the heightened tension among law enforcement officers across America after a week of violence following the deaths of two African-American men at the hands of police.

Maj. Thomas Castro told the Associated Press several general threats had been made against Dallas police, though nothing specific.

An armored vehicle was moved to near the department’s downtown headquarters late Saturday afternoon and heavily armed officers carrying rifles were seen walking nearby. Police shut down a street in front of the department’s headquarters, but members of the public were still able to walk about freely around the building. One man dropped to his knees in front of the makeshift memorial and began singing “Amazing Grace.”

Dallas Police Department spokeswoman Sr. Cpl. Monica Cordova called the security measures precautionary.