The New York Police Department has reportedly assigned three dozen elite investigators to catch the intruders who replaced the American flags on the Brooklyn Bridge with white flags early Tuesday morning. 

The New York Post reports that the officers were pulled from the department's homicide, counterterrorism, intelligence and transit units to assist in the investigation. 

The Post reported that investigators were looking for four or five men who were carrying backpacks and may have been traveling in two groups. The paper also reported that investigators have been scanning security cameras near the bridge on both sides of the East River without success. 

"We have no good images of these guys on cameras," a police source told the Post. "None of the footage captures the perpetrators of this crime."

The bleached American flags were discovered at the top of the bridge's two 276-foot high towers after dawn broke Tuesday.  The intruders would have had to climb hundreds of feet on the bridge's suspension cables before getting past locked gates and using ladders to get to the towers' apex. 

The Post reported that police have stepped up foot patrols near the towers and the bridge's pedestrian walkway and installed new security cameras on both sides of the bridge.

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